Michael J. Schirripa
Southeast Fisheries Science Center, Miami Laboratory, Sustainable Fisheries Division, 75 Virginia Beach Drive, Miami, FL 33149-1099,U.S.A.
Abstract: Based on current assessments, the Gulf of Mexico red snapper stock is severely overfished, and catch allocations to the fishery are restricted. Confounding the issue of fishing mortality on this stock from directed fishing efforts is the incidental fishing mortality on juvenile red snapper from shrimp trawling. The offshore shrimp fishery exerts considerable mortality on age 0 and 1 red snapper in the form of discarded bycatch. The Gulf of Mexico Fisheries Management Council currently uses a minimum value for spawning potential ratio (SPR) of 20% as its management objective for red snapper, however, the future management goal will likely be based on maximum sustainable yield (MSY), or a proxy thereof. Values of MSY for the directed fishery were calculated for a range of bycatch mortalities and release mortalities while assuming fixed values for biological parameters. Values for MSY for the directed fishery differed for each level of bycatch mortality for the undirected fishery. More specifically, values of MSY for the directed fishery were systematically reduced by increases in bycatch mortality from the undirected fishery. Under the assumptions outlined for this analysis, it is highly unlikely that the resource could be simultaneously fished at FMSY and maintain a 20% SPR unless bycatch mortality can be reduced by approximately 90% or more. If approximately 50% to 60% bycatch reduction is the best that can be achieved by bycatch reduction devices (BRDs), and if the fishery is fished at FMSY, then the greatest SPR value that can likely be achieved will be approximately 10%. Of the three management options, FMSY, SPR equal to 20% and bycatch reduction of 50% to 60%, only two can be achieved simultaneously, but not all three.
One of the more challenging fishery management and economic issues in the U.S. Gulf of Mexico concerns the incidental bycatch of juvenile red snapper (Lutjanus campechanus) by shrimp trawlers. Management of the red snapper resource has meant dividing the allowable fishing mortality between two competing fisheries: the directed fishery, which consists of a commercial and a recreational sector, and the undirected shrimp fishery. The directed fishery, which harvests fish that are approximately age 3 and older, is managed by way of an annual total allowable catch (TAC). Of the total TAC, 51% is allocated to the commercial sector and 49% to the recreational sector. The catch of both the commercial and recreational sector is monitored within the year and each of the fisheries is closed upon reaching their respective allocation of the TAC. Traditional management measures are also used, such as a minimum legal size as well as daily bag limits for recreational boats and trip limits for commercial boats.
In contrast, the undirected fishery, formed by the U.S. Gulf of Mexico offshore shrimp fleet, harvests age 0 and 1 red snapper in the form of bycatch. These vessels use bottom trawls to harvest shrimp, which share a propensity for the same habitat as juvenile red snapper. Although the discarded catch associated with shrimp trawls is not counted toward the TAC, it is included in the stock assessment as part of the total fishing mortality. Along with juvenile red snapper the shrimp bottom trawls also catch in varying magnitudes a multitude of other bottom dwelling species of fish, turtles, other vertebrates and invertebrates. Because there is currently no market for this bycatch, the poundage is discarded at sea. Until very recently, the shrimp fishery has not generally been restricted on the amount of bycatch. In 1991, turtle excluder devices (TED) were mandated for all offshore shrimp boats operating in the Gulf of Mexico. In 1998 all offshore shrimp boats fishing in the western Gulf of Mexico were required to use some form of bycatch reduction device (BRD) as well. Several types of BRDs have been "certified" by the U.S. fishery management authorities as reducing red snapper bycatch by 30% to 50% with an approximate 4% to 6% percent reduction in shrimp loss.
The possible role of shrimp bycatch mortality as an agent leading to declines in red snapper abundance was raised by Moe (1963) and Bradley and Bryan (1976). Both studies noted that red snapper fishermen believed shrimp bycatch of juvenile snapper led to declines in overall red snapper abundance. Historic assessments of red snapper abundance have arrived at the conclusion that the stock is severely overfished (Goodyear 1990, 1995). More recent assessments (Schirripa and Legault 1997, Schirripa 1998) have shown that the recovery of the red snapper fishery is more dependent upon the control of mortality from the undirected fishery than the mortality which occurs in the directed fishery, given the current management systems in place. The Gulf of Mexico Fisheries Management Council (GMFMC) has made it clear that both the directed and undirected fisheries need to persist, therefore trade-offs must be made.
Historically, the GMFMC has used a minimum value for spawning potential ratio (SPR) of 20% as its definition of overfishing and as its management objective for red snapper. However, the recent changes in the language of the Magnuson-Stevens Fishery Conservation and Management Act (U.S. Congress 1996) have required that the overfished threshold be based on the spawning stock size that would support maximum sustainable yield (MSY). However, Goodyear (1996) showed how changes in fishing mortality by age changed the calculation of MSY (i.e. MSY is conditional on the fishing selectivity). In this paper, this concept is used to demonstrate how changes in shrimp bycatch mortality of the undirected fishery change the calculation of MSY, FMSY, and SPR for the directed fishery. This work is not intended to calculate a working value of MSY for the red snapper stock, but rather to show how calculations of MSY for this fishery respond to systematic variations in release mortality, age at entry into the directed fishery, and to bycatch reduction in the undirected fishery.
The biological characteristics estimated for Gulf of Mexico red snapper in Goodyear (1995) were used in this analysis. A Beverton-Holt stock recruitment function was used to estimate recruitment from population fecundity:
R = P / (P + ß);
where R is recruitment in numbers of survivors at age 0, and P is parental fecundity. The inverse of the maximum number of recruits possible () was set at 4.09E-09, and the slope of the stock-recruitment curve at the origin (ß) was set at 1.74E+05. Natural mortality was 0.50 for age 0, 0.30 for age 1, and 0.10 for the remaining ages 2 to 50. Growth and fecundity were constant functions of age.
Because the directed and the undirected fisheries are managed separately, fishing mortality for the two sectors were modelled independently of each other. Bycatch fishing mortalities applied were those estimated in the most current stock assessment (Schirripa and Legault 1997) and were 0.59 for ages 0, and 1.29 for age 1. Bycatch mortality was included in the calculation of total mortality, but not in the calculation of yield. A range of bycatch mortality reductions from 0% to 100% was examined.
Recruitment into the directed fishery was considered to be knife-edge (i.e. fish at a given age were assumed to be either entirely available or entirely unavailable to the fishery). Ages at entry into the directed fishery examined, ranged from two to seven years. Release mortalities from the directed fishery examined were 0%, 20%, and 33%. MSY was calculated as a function of the minimum age of recruitment into the directed fishery, undirected fishery bycatch, and directed fishery release mortality. MSY was calculated by first calculating the yield-per-recruit for a given fishing mortality and a stable age distribution. Eggs-per-recruit was subsequently calculated from the resulting exploited age distribution and the fecundity function. Applying the stock-recruitment function to the eggs-per-recruit the calculation was then solved for the total number of eggs, recruits, and yield. MSY was calculated by interactively searching for the directed fishing mortality that resulted in the largest equilibrium catch in weight (FMSY) to the directed fishery. The spawning potential ratio (SPR), the ratio of lifetime reproductive potential of the average female in the fished stock (Pfished) to that in an unfished stock (Punfished), was estimated as described in Goodyear (1993), such that SPR = Pfished/Punfished. All estimates of MSY, FMSY, and SPR were made for equilibrium conditions. Consequently, all isopleths in the figures correspond to fishing at MSY.
Values of MSY for the directed fishery differed for each level of bycatch mortality in the undirected fishery (Fig. 1a). More specifically, values of MSY for the directed fishery were systematically reduced by increases in bycatch mortality from the undirected fishery. Age at entry into the directed fishery had much less of an influence on the calculation of MSY than did changes in bycatch reduction as indicated by the near vertical lines in Fig. 1b.
Conversely, calculations of FMSY (directed fishery) for a given age at entry into the directed fishery were virtually unaffected by the amount of bycatch mortality (Fig. 1c). As age at entry into the directed fishery increased so did FMSY , and the yield resulting from FMSY.
The nearly vertical relationship between percent bycatch reduction and age at entry indicate that reducing bycatch has a much greater effect on increasing SPR than increasing the age at entry into the directed fishery (Fig. 1d). For a given level of bycatch reduction, increasing age-at entry into the directed fishery decreased the SPR. At first this may seem counter intuitive. However, the relationship between bycatch reduction and age at entry (Fig. 1c) shows that increasing age at entry into the directed fishery must be accompanied by an increase in fishing mortality in order to maintain the yield at MSY. This increase in fishing mortality then results in the decrease in SPR as is shown in Fig. 1d. Although the SPR decreases with increasing age at entry to the directed fishery, an increase in yield is also realised. This is shown in Figs. 1a and 1b as the relative MSY increases with increased age at entry into the directed fishery for a given level of bycatch reduction.
Release mortality decreased the absolute value of the yield resulting from fishing at MSY from 2.24E+08 lb. for 0% release mortality (Fig. 1a), to 1.82E+08 LB for 20% release mortality (Fig. 2a), and to 1.65E+08 LB for 33% release mortality (Fig. 3a). This decreased yield was the result of release mortality decreasing FMSY, as shown by comparing Figs. 1c, 2c, and 3c. Since release mortality adds to the overall fishing mortality but not to the resulting yield, fishing mortality must be decreased in order to compensate for those fish killed that are not accounted for in the yield. Release mortality also had the affect of reducing the usefulness of increasing the age at entry into the directed fishery as a means of increasing MSY (Figs 2b and 3b).
As expected, release mortality decreased the usefulness of increasing the age at entry into the directed fishery as a means of increasing the SPR. Assuming 22% and 33% release mortality, increases in age at entry to the directed fishery resulted in very small increases in MSY (Figs. 2b and 3b) as well as SPR (Figs. 2d and 3d). However, gains realised from reductions in bycatch mortality remained nearly as large as with 0% release mortality.
In order to manage the directed fishery for red snapper effectively it is necessary to monitor and manage the undirected fishery (i.e. the shrimp fishery bycatch). This is because MSY is not a unique number of pounds or number of fish, but is dependent upon, amongst other things, a value for bycatch mortality for the undirected fishery as well as the age at entry for the directed fishery. If regulations are put into place that change bycatch mortality, or the selectivity pattern of the directed gear, then the calculations of MSY will change as well.
The results herein indicate that it is unlikely for the red snapper fishery to be simultaneously fished at FMSY and maintain a 20% SPR unless bycatch mortality can be reduced by approximately 90% to 100%. If 50% to 60% bycatch reduction is the best that can be achieved by BRDs, and if the fishery is managed for MSY, then the greatest SPR value that is likely to be achieved will be approximately 10%. Only two of the three management options, FMSY, SPR of 20%, and bycatch reduction of 50% to 60%, are likely to be achieved simultaneously.
These analyses show that failure to decrease bycatch mortality in the shrimp fishery will result in the need to further regulate the directed fishery if current or expected future fishery management goals are to be achieved. More regulations will ultimately lead to the directed fishery (as it now exists) fishing further below the fleet's full capacity. It is likely that additional trade-offs will need to be made between the level of bycatch mortality in the undirected fishery and allowing the directed fishery to fish at its full potential.
Importantly, this analysis makes no assumptions concerning the minimum value of SPR required for stock persistence. The fact that equilibrium estimates of SPR can be calculated does not assure that fishing the stock at those levels could continue indefinitely. The term "overfishing", as used by the GMFMC, is a rate or level of fishing mortality that jeopardises the capacity of a fishery to produce the maximum sustainable yield on a continuing basis. Currently, the GMFMC defines overfishing to have taken place when the SPR falls below 20 percent. In order to maintain a 20% SPR and maintain the directed fishery at FMSY, bycatch would need to be reduced by approximately 90% of that currently estimated. If, however, bycatch mortality can only be reduced by approximately 50%, then it is unlikely that the directed fishery can be allowed to fish at FMSY if the SPR is to be maintained above 10%.
I thank Chris Legault for suggestions and help with calculations.
BEVERTON, R.J.H., & HOLT, S.J. 1957. On the dynamics of exploited fish populations. Great Britain Ministry of Agriculture Fisheries and Food 19.
BRADLEY, E. & BRYAN, C.E. 1975. Life history and fishery of the red snapper (Lutjanus campechanus) in the north-western Gulf of Mexico: 1970-1974. Proceedings of the Gulf and Caribbean Fisheries Institute, 27: 77-106.
GOODYEAR, C.P. 1990. Status of red snapper stocks of the Gulf of Mexico report for 1990, National Marine Fisheries Service, Southeast Fisheries Center, Miami Laboratory, Miami CRDC89/90-05.
GOODYEAR, C.P. 1995. Red snapper in U.S. waters of the Gulf of Mexico, National Marine Fisheries Service, Southeast Fisheries Science Center, Miami Laboratory, Miami MIAC95/96-05.
MOE, M.A. 1963. A survey of offshore fishing in Florida. Professional Paper Series Marine Laboratory Florida, 4: 1-117. St. Petersburg, Florida.
RICKER, W.E. 1975. Computation and interpretation of biological statistics of fish populations. Fisheries Research Board of Canada Bulletin 191.
SCHIRRIPA, M.J. & LEGAULT, C.M. 1997. Status of the red snapper in U.S. waters of the Gulf of Mexico: updated through 1996. Southeast Fisheries Science Center, Miami Laboratory, Miami MIAC97/98-05.
SCHIRRIPA, M.J. 1998. Status of the red snapper in U.S. waters of the Gulf of Mexico: updated through 1997. NOAA/NMFS Sustainable Fisheries Division Contribution, SFD-97/98-30.
U.S. CONGRESS. 1990. Magnuson Fishery Conservation and Management Act (PL 94-265, as amended through November 28, 1990. Government Printing Office, Washington, D.C.
Figure 1a. Relative maximum sustainable yield (scaled to the maximum over all combinations) as a function of reductions in bycatch mortality and age at entry into the directed fishery assuming 0% release mortality for the directed fishery. Figure 1c. FMSY isopleths as a function of reductions in bycatch mortality and age at entry into the directed fishery assuming 0% release mortality for the directed fishery. Figure 1b. Relative maximum sustainable yield (scaled to the maximum over all combinations) isopleths as a function of reductions in bycatch mortality and age at entry into the directed fishery assuming 0% release mortality for the directed fishery. Figure 1d. SPR isopleths as a function of reductions in bycatch mortality and age at entry into the directed fishery assuming 0% release mortality for the directed fishery Figure 2a. Relative maximum sustainable yield (scaled to the maximum over all combinations) as a function of reductions in bycatch mortality and age at entry into the directed fishery assuming 20% release mortality for the directed fishery. Figure 2c. FMSY isopleths as a function of reductions in bycatch mortality and age at entry into the directed fishery assuming 20% release mortality for the directed fishery. Figure 2b. Relative maximum sustainable yield (scaled to the maximum over all combinations) isopleths as a function of reductions in bycatch mortality and age at entry into the directed fishery assuming 20% release mortality for the directed fishery. Figure 2d. SPR isopleths as a function of reductions in bycatch mortality and age at entry into the directed fishery assuming 20% release mortality for the directed fishery. Figure 3a. Relative maximum sustainable yield (scaled to the maximum over all combinations) as a function of reductions in bycatch mortality and age at entry into the directed fishery assuming 33% release mortality for the directed fishery. Figure 3c. FMSY isopleths as a function of reductions in bycatch mortality and age at entry into the directed fishery assuming 33% release mortality for the directed fishery. Figure 3b. Relative maximum sustainable yield (scaled to the maximum over all combinations) isopleths as a function of reductions in bycatch mortality and age at entry into the directed fishery assuming 33% release mortality for the directed fishery. Figure 3d. SPR isopleths as a function of reductions in bycatch mortality and age at entry into the directed fishery assuming 33% release mortality for the directed fishery.
Ian A. Knuckey1, Chris Grieve2 and David C. Smith1
1 Marine and Freshwater Resources Institute, PO Box 114, Queenscliff, VIC 3225, Australia
2 Australian Fisheries Management Authority, Box 7051, Canberra Mail Centre, ACT 2610, Australia.
Abstract: The South East Fishery is a complex, multi-species, multi-gear scalefish fishery which operates off south-eastern Australia. Monitoring of the fishery over the last 50 years has evolved from ad hoc research programmes conducted by several State and Commonwealth agencies to a statistically rigorous monitoring programme co-ordinated by the Australian Fisheries Management Authority (AFMA). The goals of this "Integrated Scientific Monitoring Programme" (ISMP) are well defined within AFMA's management objectives for the fishery. This paper describes the evolution of the ISMP and outlines the methods used to design the sampling strategy to achieve its objectives. Although voluntary, vessel participation rates in the ISMP are high, largely because information collected by the programme is not used for compliance purposes. Instead, the role of the ISMP is clearly defined as a means of collecting extensive information for use in stock assessment and management. The issues and implications of this type of approach to a monitoring programme are discussed.
The South East Fishery (SEF) is a complex, multi-species, multi-gear fishery which provides most of the fresh fish for the markets in south-eastern Australia. It has an annual landed value of around AUD $50 million (Tilzey 1998). Part of the complexity of the SEF arises from the variety of fishing methods, encompassing the trawl sector which includes otter trawl, Danish seine and midwater trawl, and the non-trawl sector which includes dropline, demersal longline, trap and gillnet. These sectors extend from the low water mark to the outer limit of the 200 N.M. Australian Fishing Zone (AFZ) off the states of South Australia (eastwards from Kangaroo Island for the trawl sector), Victoria and Tasmania. In New South Wales, the trawl sector extends from the 3 N.M. state limit to the outer limit of the AFZ south of Barrenjoey Point, and the non-trawl sector extends from outside 80 N.M. to the outer limit of the AFZ south of Fraser Island in Queensland.
Reflecting this large geographical area and the range of fishing methods, the fishery operates in a variety of habitats from shallow coastal waters to depths of over 1000 m off the continental shelf and a large range of species are landed, including over 100 species of fish and invertebrates (Klaer and Tilzey 1994). Sixteen of these species (blue grenadier, Macruronus novaezelandiae; ling, Genypterus blacodes; orange roughy, Hoplostethus atlanticus; redfish Centroberyx affinis; mirror dory, Zenopsis nebulosis; John dory, Zues faber; ocean perch, Helicolenus percoides; tiger flathead, Neoplatycephalus richardsoni; school whiting, Sillago flindersi; silver trevally, Pseudocaranx dentex; jackass morwong, Nemadactylus macropterus; gemfish, Rexea solandri; blue eye trevalla, Hyperoglyphe antarctica; blue warehou, Seriolella brama; spotted warehou, Seriolella punctata and royal red prawn, Haliporoides sibogae) are under quota management and constitute over 80% of the landed catch and about 90% of the landed value (Tilzey 1998).
Over the last 20 years, the fishery has expanded considerably and the various fish stocks have been subjected to increased fishing pressure by all sectors. Concern over the potential for overfishing has prompted substantial changes in the management regime and in conjunction, there has been an increased need for information on the biology and population dynamics of the various species for use in stock assessments. A range of research and monitoring programmes have been undertaken to meet this need. This paper outlines the changes in management of the SEF that have occurred in recent years and links them to the evolution of the various research and monitoring programmes.
The trawl sector of the SEF is one of Australia's oldest commercial fisheries. It began in 1915 in the waters off New South Wales (NSW) when three steam trawlers were purchased from England by the NSW Government (Fairbridge 1948). In lieu of Commonwealth management prior to the mid-1980s, it was an open-access fishery managed by several State governments using a variety of regulations on mesh sizes, minimum legal lengths and area closures. During the 1970s and 1980s, the trawl fleet expanded outwards and southwards as new target species, fishing grounds and fishing techniques were developed (Graham et al. 1982, Wankowski 1983). A marked increase in fishing effort and resultant pressure on fish stocks prompted the Commonwealth government to limit entry to the fishery in 1985. Management arrangements by way of input controls were later formalised in a statutory plan of management. These arrangements included restrictions on vessel length and fishing capacity - "unitised" through a formula based on hull size and engine capacity. These units were transferable and boat replacement forfeiture provisions applied in an attempt to maintain or reduce overall fishing capacity.
Pressure on the input control regime intensified during the late 1980s as a result of two unrelated events in the fishery. Large, spawning orange roughy aggregations were discovered off the east coast of Tasmania (Lyle 1994) at around the same time as a recruitment failure caused the collapse of the eastern gemfish fishery (Rowling 1994). This led to an overall shift of trawl licences and units from the east coast operators using small wooden vessels (> 20 m Overall Length) to larger capacity steel-hulled vessels working further south. Meanwhile, the rest of the fishery was characterised by a `persistent and worsening economic situation while management relied on reducing economic efficiency' (Anon. 1989). Ultimately, the input control regime failed to relieve pressure on fish stocks and reduce over-capitalisation in the fishery, and it was replaced on 1 January 1992 by the South East Trawl Fishery (Individual Transferable Quota) Management Plan. Under this plan, total allowable catches (TACs) were introduced for 16 of the major species and individual transferable quotas (ITQs) were allocated to eligible operators. Limited entry, mesh sizes and vessel length restrictions were maintained in the regulations. The fishery has continued to be managed in substantially the same manner under a system of fishing permits (with no vessel length restrictions). A new management plan entitled the South East Trawl Fishery Management Plan 1998 will grant Statutory Fishing Rights based on ITQs and fishing permits will be issued to eligible operators sometime during 1999.
Detailed information on the origins of the non-trawl sector is not available, but prior to 1985, it was effectively an open access fishery. In July 1985, a freeze was placed on issuing new licences, but by this time thousands of non-trawl licences existed in Commonwealth waters. Many of these licences were not used to any great extent, creating a large pool of latent effort. About this time, gillnet operators in the southern shark fishery were brought under input controls which restricted fishing effort by a system of gear units (Walker et al. 1998). This, in turn, also reduced fishing effort targeted at scalefish. In 1993, more specific limited entry criteria and long-term management arrangements were developed for the non-trawl fishery which reduced the number of licences (now termed fishing permits). On 1 January 1997 the south east non-trawl fishery was formally established, with fishing permits being granted to operators who had successfully met the entry criteria. By this time, the number of permits had been reduced from thousands to less than 170. As a further refinement of the management arrangements, on 1 January 1998, ITQs for blue warehou, blue eye trevalla and ling were introduced to the non-trawl sector of the SEF.
Under Section 3 of the Fisheries Management Act 1991(Commonwealth), AFMA is required to pursue the following objectives in the performance of its functions:
- Implementing efficient and cost-effective fisheries management on behalf of the Commonwealth;
- Ensuring that the exploitation of fisheries resources and the carrying on of any related activities are conducted in a manner consistent with the principles of ecologically sustainable development and the exercise of the precautionary principle, in particular the need to have regard to the impact of fishing activities on non-target species and the long term sustainability of the marine environment;
- Maximising economic efficiency in the exploitation of fisheries resources;
- Ensuring accountability to the fishing industry and to the Australian community in AFMA's management of fisheries resources; and
- Achieving government targets in relation to the recovery of the costs of AFMA.
To assist AFMA in the pursuit of the above objectives, particularly (2), on ecologically sustainable development, the Integrated Scientific Monitoring Programme (ISMP) was developed to provide essential data on the SEF that were not available through mandatory logbooks or catch landing monitoring systems. It was set up as a cornerstone of the SEF's Strategic Research Plan, to provide extensive biological information for stock assessments by the South East Fishery Assessment Group (SEFAG) and other individual species assessment groups. These assessments feed through to AFMA's total allowable catch (TAC) setting process via Management Advisory Committees (MACs), which are partnerships between AFMA, the fishing industry, researchers, State governments and environmental or community groups.
Monitoring of the size distributions of the landed catch has been conducted for over 50 years. It commenced in 1941 as part of a Commonwealth Scientific Industrial Research Organisation (CSIRO - then CSIR) research project on what was then the East Coast Trawl and Danish Seine Fishery (Blackburn 1978). Over 1 million fish were measured during the period 1945/46 to 1966/67 by the same person using a standard protocol (Blackburn 1978).
The expansion of the fishery during the 1970s and the discovery of orange roughy aggregations during the 1980s led to an increase in the number and extent of research and monitoring programmes in the SEF. Considerable monitoring of the biological characteristics of SEF species was undertaken by State fisheries agencies (Table 1). Improved catch and effort information became available through the introduction of a per-shot logbook for trawl and Danish seine vessels in late 1985. A number of trawl surveys and fisheries studies were also conducted by various State and Commonwealth agencies during this time. Overall, however, there was little co-ordination of these research programmes.
Table 1. Summary of monitoring and research projects undertaken in the SEF up to the commencement of the SMP in 1993.
|Institution||Period and Research Type||Indicative references|
|Tasmanian Fisheries||Port measuring 1978 - 1993
Fishery projects and trawl surveys 1980s
|Wilson et al. (1984)
Lyle et al. (1991)
Lyle and Ford (1993)
|Victorian Fisheries||Port measuring 1981 - 1993
Fishery projects and trawl surveys 1977 - present
Wankowski and Moulten (1986)
Smith et al. (1995)
|NSW Fisheries||Port measuring 1975 - 1991
Fishery projects and trawl surveys 1975 - present
|Graham and Bell (1989)
Kapala Cruise Reports
|CSIRO||Port measuring 1941 - 1967
Fishery projects and trawl surveys 1984 - present
Blaber et al. (1985)
Bulman et al. (1991)
CSIRO and TDPIF (1996)
|Commonwealth||Trawl surveys late 1970s
Logbook programme (Australian Fisheries Service and AFMA)
|Anon. (1977, 1979)|
Following the introduction of ITQs in 1992, Tilzey (1994) argued that greater discarding of quota species would be inevitable. Most of the previous research was directed towards monitoring landed catches of commercial vessels or was based on catches by chartered or research vessels. As such, there was little information collected routinely on discarding during normal commercial fishing operations. The potential for increased discarding and little data on existing practices led to the development of the Scientific Monitoring Programme (SMP) during 1992 by the Bureau of Resource Sciences (BRS).
This programme ran from 1993 to 1995 and was co-ordinated by a steering committee comprising representatives from industry, AFMA, BRS, CSIRO, and State fisheries agencies (NSW, Victoria and Tasmania) (Garvey 1996; Chesson 1997). The primary objective of the SMP was to provide information particularly on discards and bycatch for stock assessment of the SEF. At-sea observers were employed to collect information on species composition and length-frequency of the retained and discarded catch of trawlers and Danish seine vessels. At the same time, the New South Wales Fisheries Research Institute (NSWFRI) conducted a project on the interaction between fish trawling (in NSW) and other commercial and recreational fisheries (Liggins 1996). This project was basically an observer programme run on SEF trawlers working out of the NSW ports of Eden, Ulladulla and Newcastle/Tuncurry and had objectives and on-board sampling activities similar to those of the SMP. Between the NSW project and the SMP, on-board monitoring was being conducted throughout most of the SEF. Port-based fish measurement and otolith collection, however, continued to be conducted by the various State fisheries agencies although there was some Commonwealth funding support.
One of the significant improvements in the level of collaboration between the various agencies began in 1991 when a specialist unit, the Central Ageing Facility (CAF) was established (Morison et al., 1998). The unit undertook ageing of key species in the SEF, replacing the somewhat ad hoc (and often duplicated) monitoring of the age composition of catches.
A review of the SMP in 1995 recommended that the various elements of monitoring in the SEF should be combined into a single integrated programme; the "ISMP". The term "Integrated" for the purposes of this programme encompassed the monitoring of trawler catches at-sea and in ports, in areas covered by the SMP and NSWFRI project. One of the key issues was the lack of an overall statistical framework for determining the efficient allocation of sampling effort towards achieving target precision in estimates of the quantities of interest, particularly discard rates. There was also duplication of some aspects of data management and analysis. Furthermore, there was increasing negative publicity and public concern about perceived wastage of resources by trawlers and potentially detrimental effects on the marine environment.
It was against this background, particularly the need for increased statistical rigour and a more consistent approach across the whole fishery, that the design of an Integrated Scientific Monitoring Programme was commissioned by AFMA in 1996. The design of the new ISMP was undertaken by the National Institute of Water and Atmospheric Research Ltd., New Zealand (NIWA) and the Marine and Freshwater Resources Institute (MAFRI) during 1996/97. The design was externally reviewed, modified as appropriate, and implemented during 1998.
During the period in which the ISMP was being designed, an "interim" SMP was implemented to continue the time series of data collection and ensure that the pool of experienced observers was maintained (Garvey 1998). It did not include at-sea monitoring of the non-trawl component of the fishery although a small amount of port-based monitoring of non-trawl catches was undertaken. The programme was managed by AFMA, with Victoria and NSW collecting the information and BRS managing the databases. Although an interim arrangement, it was a major improvement on the previous SMP, and continued for two years until the ISMP was introduced in 1998.
As suggested by Tilzey (1994), the SEF, under quota management, has witnessed considerable discarding of quota species (Liggins 1996, Knuckey and Liggins 1999) for a variety of reasons (Liggins and Knuckey 1999) and this has had important implications for stock assessments of these species. Thus, to provide essential information for stock assessment, the objectives of the ISMP design were to use at-sea and port sampling to provide estimates of:
- The total catch (retained and discarded) of quota species;
- The total catch (retained and discarded) of other species, and
- The size/age composition of the total catch (retained and discarded) for selected species.
Using all available data, a rigorous evaluation of the SEF was undertaken to determine the most practical and cost-effective means of achieving these objectives. Greatest emphasis was placed on the estimation of discard rates (the most expensive component of such a programme) in the trawl and Danish seine fleets for which there was the most information.
Characteristics of the fishery were described by combining the extensive datasets containing logbook and landings records. Trawl landing records included almost 80,000 t landed from 23,700 trips, and Danish seine records represented landings of 8,000 t from 5,600 trips. The logbook data included spatial information and provided the foundation for determining strata based on species, gear and port groups. A further factor considered was the size of vessel landings (high volume and low volume). Three species had clear target fisheries: orange roughy, spawning blue grenadier and royal red prawns. A potential problem categorising trips for species forming mixed species catches was resolved by grouping these quota species into "inshore" and "offshore" groups (equivalent to shelf and slope), reflecting the difference in species assemblages with depth. Four port groups were chosen: NSW, Eden/Lakes Entrance, Tasmania and South west. A total of 14 strata were consequently defined, based on gear type, main species caught, port group and size of landings (Fig. 1, Tab. 2).
Previous on-board monitoring data from the SMP (Garvey 1996), NSWFRI (Liggins 1996) and the interim SMP (Knuckey 1997) were used to determine discard rates for quota and other species in each strata (see Table 3 for a summary of percentage discarded by species). Species were grouped by discard rate into three groups; <5%, 5-20%, and >20% and simulation modelling was used to determine the number of trips required in each strata to achieve a range of values of target coefficient of variation (CV) - the precision of the estimate. In each case, target CVs was related to the discard rate. For example, the target CV for species with low discard rates could be higher than those for species with high discard rates with little effect on total catch estimates. All non-quota species were combined in analyses as `other species' for which target CVs were set at relatively high levels. As obtaining a low CV for this group required a particularly high sampling intensity and as it was unlikely in practical terms that any stock assessments would be carried out on these species, precise estimates of discard rates were determined to be less critical than those of quota species.
The numbers of at-sea sampling trips were calculated for four options, designated high, medium-high, medium-low and low, based on their respective sampling intensities which ranged from approximately 250 to 70 sea-days. Each option had a set of specified CVs for the discard rates (the percentage discarded) of quota species, which was determined by the number of trips per strata. An agreed sampling strategy was then determined based on budget and target CVs.
Discard rates for the non-trawl sector were not considered. Data were limited for this sector but discard rates were considered to be small. An independently funded pilot study has since been initiated to determine the extent to which at-sea sampling will be necessary in the non-trawl sector.
Simulation modelling was used to assess the sampling intensity required to develop both length and age-length keys for each species with CVs under 10%. For length, the modelling was undertaken to provide a matrix of the number of samples and the corresponding number of fish in each sample (Fig. 2). Length sampling was based on the same strata as for discards. Although a significant amount of length data is collected at sea, the collection of length and age data by port-based staff is far more cost effective than by observers. The majority of this information is therefore derived from the port landings, with data regarding the discarded catch being collected at sea by observers. The age-length keys (Fig. 3) were developed across all strata on the general assumptions that there were negligible differences in growth between strata and that the costs involved in ageing large numbers of fish sampled by stratum was prohibitive.
By 1998, the ISMP had evolved into a co-ordinated, statistically rigorous monitoring programme, which incorporated both at-sea and port-based sampling undertaken throughout the SEF.
In common with the fishery, the ISMP has changed considerably over the last decade and will continue to evolve as it caters to the various needs and pressures of industry, management, research and other interest groups. In so doing, a variety of issues arose which needed to be addressed to maintain the effectiveness of the ISMP as an important research and management tool.
One of the initial and most fundamental issues, which had to be tackled in the development of the ISMP, was whether acceptance of ISMP scientists on board vessels would be voluntary or mandatory. Obviously, this issue was closely linked to whether on-board data were to be used in a compliance role or just for biological and stock assessment purposes.
Figure 1. The geographical extent of Australia's Southeast fishery, showing the major fishing ports and the 14 strata highlighted in the design of the ISMP (Smith et al. 1997). The trawl and non-trawl sectors extend from the low water mark to the outer limit of the 200 N.M. Australian Fishing Zone (AFZ) off the states of South Australia (eastwards from Kangaroo Island for the trawl sector), Victoria and Tasmania. In New South Wales, the trawl sector extends from the 3 N.M. state limit to the outer limit of the AFZ south of Barrenjoey Point, and the non-trawl sector extends from outside 80 N.M. to the outer limit of the AFZ south of Fraser Island in Queensland.
Table 2. Stratification of the SEF based on gear type, main species caught, port group and size of landings. High catch vessels are those whose mean landing weight per trip over all fisheries is over 5 t. Low catch vessels are all others (after Smith et al. 1997).
|Gear||Port group||Defining species|
|NSW INSH all||O. Trawl||NSW||Spotted warehou, blue warehou, tiger flathead, jackass morwong, silver trevally, John dory and redfish|
|NSW OFFSH all||O. Trawl||NSW||Blue grenadier (non-spawning), gemfish, ling, ocean perch, mirror dory|
|NSW RRP all||O. Trawl||NSW||Royal red prawn|
|EDL DS all||D. Seine||EDEN LAKES||School whiting, tiger flathead|
|EDL INSH hv||O. Trawl, high catch vessels||EDEN LAKES||Spotted warehou, blue warehou, tiger flathead, jackass morwong, silver trevally, John dory and redfish|
|EDL INSH lv||O. Trawl, low catch vessels||EDEN LAKES||Spotted warehou, blue warehou, tiger flathead, jackass morwong, silver trevally, John dory and redfish|
|EDL OFFSH all||O. Trawl||EDEN LAKES||Blue grenadier (non-spawning), gemfish, ling, ocean perch, mirror dory|
|TAS ORO all||O. Trawl||TAS||Orange roughy|
|TAS OTH all||O. Trawl||TAS||All species excluding roughy and spawning grenadier|
|TAS SBG all||O. Trawl||TAS||Blue grenadier (spawning)|
|SW OTH hv||O. Trawl, high catch vessels||SW||All species excluding roughy and spawning grenadier|
|SW OTH lv||O. Trawl, low catch vessels||SW||All species excluding roughy and spawning grenadier|
|SW ORO all||O. Trawl||SW||Orange roughy|
|SW SBG all||O. Trawl||SW||Blue grenadier (spawning)|
Figure 2. Simulation modelling was used to assess the sampling intensity required to develop length distributions for each species with coefficients of variation (CVs) under 10%. The practical requirements of fish measuring determined that the target-sampling regime required 50 samples of approximately 100 fish per sample to achieve a CV of between 5 and 10%. Sampling regimes varied slightly for the different species (after Smith et al. 1997).
Following discussions between industry, management and researchers, AFMA decided that the ISMP would not have any compliance-related objectives and that its primary role would be the collection of biological and other scientific information. Alternative compliance methods were deployed in the fishery, which were not based on the use of observers. It was also determined that participation of vessels in the ISMP would be voluntary with only partial at-sea coverage of all trawl shots. This decision had important implications for how the ISMP was to achieve the sampling intensity and fleet coverage it required. Basically, it was essential that the ISMP develop and maintain strong industrial relationships so that a wide range of vessels from each of the major ports would be willing to participate in the ISMP. A variety of mechanisms have been introduced which strengthen these relationships, including regular reports to industry summarising ISMP activities, and a system of informal port-visits, where managers, researchers (including ISMP staff) and industry meet to discuss various aspects of the fishery. The regular contact of ISMP staff with skippers and crew of vessels working from their port also ensures close working relationships.
Table 3. Summary of scientific monitoring project data showing percentage discards by quota species and all other species combined. Source: SMP database. Note: excludes data from NSWFRI by-catch project.
|Species||Shots Sampled||Retained catch (kg)||Discarded catch (kg)||Total catch (kg)||Percentage discarded|
In a voluntary programme, this liaison is vital to ensure that coverage is sufficient to meet the statistical requirements of the ISMP. Although, in general this has not been a problem, there have been a couple of strata where participation rates have prevented the achievement of target coverage levels. In most instances this has been addressed by specific meetings between ISMP staff and skippers to improve coverage. In the rare cases where this has been unsuccessful it has been necessary to accept that discard CVs for some species in a particular stratum may end up higher than projected. As evidence of the success of the voluntary participation nature of the programme, ISMP field scientists have access to over 60% of the SEF trawl fleet, a figure that has steadily increased over recent years. Nevertheless, observer coverage of the fleet is not complete, so it is important to establish whether fishing practices change when observers are present. In their study off New South Wales, Liggins et al. (1997) found that estimates of catch and size distribution were unaffected by significant bias due to the presence of observers. The composition and size frequency of retained catches monitored from vessels partaking in the ISMP can be compared to those from the more extensive monitoring of landed catches, including vessels which do not accept ISMP observers, to ensure such biases remain low.
Overall, both research and compliance play vital roles in the sustainable management process. Where these roles are separate, such as in the ISMP, it is imperative that objectives are openly stated and made very clear to the industry prior to their involvement.
Figure 3. Simulation modelling was used to assess the sampling intensity required to develop age-length keys for each species with coefficients of variation (CVs) under 10%. The practical requirements of fish ageing determined that sampling was undertaken across all strata. The example shown is the mean weighted coefficient of variation (MWCV) for western gemfish against the sample size of the age-length key (after Smith et al. 1997).
One of the most important aspects of the ISMP is the operators' trust in the confidentiality of the data. There are always concerns by operators that their vessels' confidential information (e.g. catches, positions etc.) recorded by field scientists may be made available to other operators, enforcement officers or government agencies. If this were to happen, trust in the ISMP would diminish and many operators would refuse to allow field scientist aboard their vessels. To ensure that the integrity of ISMP data is maintained, summaries are always aggregated over five or more vessels. Where stock assessment analyses require specific vessel-by-vessel information, vessel names are coded by the ISMP prior to being made available to the scientist. Importantly, both the ISMP contractors and the scientists undertaking the stock assessments are bound by confidentiality agreements. Results of the stock assessments are only reported to AFMA in an aggregated form, which is more than adequate to meet AFMA's `scientific' objectives for the ISMP. Furthermore, the raw data are not seen or kept by AFMA. Instead, the data are held by both the contractors and the Commonwealth's BRS under a `stewardship' arrangement. Summaries of the ISMP data are provided to Industry on an annual basis and include information on catch size, distribution and discard rates. Although this information is not specifically released to the general public, it is available in a range of reports in both the grey and published literature.
Because the fishery spans four states and is managed by the Commonwealth, there is a continued need for close co-operation and collaboration between these fishery agencies. Memoranda of understanding have been established between the various State and Commonwealth agencies which allow the transfer of data for scientific purposes, whilst ensuring its confidentiality. Where ISMP data are required, a letter stating the intended use of the data needs to be sent to AFMA and approved prior to the release of the data by the ISMP contractors. As mentioned previously, most of the SEF stock assessments are undertaken by SEFAG, which includes members from all of these agencies as well as the industry. As a result, the collaboration between researchers and managers from the various agencies together with the industry is usually very good.
In a fishery as complex as the SEF, the industry often has general concerns which are inevitably more related to the politics or management of the fishery than any particular aspect of the ISMP. Nevertheless, they do impact on the operator's willingness to participate in the ISMP and often warrant consideration by those involved in the fishery. Therefore, another important, and possibly understated, advantage of the collaboration of the ISMP with industry is that it provides a mechanism by which such concerns can be related back to fishery managers and researchers in a less formal forum than stock assessment groups or management committees.
Insurance and possible Marine Board violations associated with the carrying of ISMP field scientists on commercial fishing vessels proved to be of particular concern to the industry. The relevant State marine agencies and insurance companies were contacted to help clarify and resolve these issues. They stipulated that as long as a vessel had sufficient life raft capacity and life jackets to cover the number of persons on board and was not overloaded to a capacity that was considered unsafe, then there was no issue with carrying additional fisheries research staff. With respect to insurance, advice from three major insurers of fishing vessels was that operators' insurance cover would not be affected by the carriage of ISMP observers and that operators' Protection and Liability insurance would cover any liability should a field scientist be injured as a result of a negligent act. They did advise, however, that individual operators should contact their own insurers to extend their Protection and Liability cover for field scientists, which could be done at no additional cost to their policy. In addition to the vessels' insurance, as State government employees, the ISMP field scientists are covered by both a comprehensive work cover policy and a public liability policy when on board vessels. To help vessel operators understand these insurance and safety issues, field scientists provide vessel operators with a package of papers prior to boarding (Sporcic and Knuckey 1998). This package contains evidence of their contract of employment (including a confidentiality clause), current work cover policy, sea safety and first aid qualifications, relevant letters from the marine board and insurance agencies and a signed safety checklist stating that the field scientist has been acquainted with the important safety aspects for each vessel (e.g. the whereabouts of life raft, life jacket, EPIRB, fire safety equipment etc).
A period of training and education is provided to all ISMP field staff. To be employed, they generally have extensive sea-going experience and a scientific background, but are further trained in aspects of safety, sampling procedures, species recognition, computing and data recording and entry. The on-board observers are required to have completed a registered shipboard safety course and obtain an advanced first aid qualification prior to boarding a vessel. An experienced observer accompanies any new staff on their first trip to ensure they work well on trawlers, exhibit safe working practices and are skilled in biological monitoring at sea. An Operation and Procedures Manual (Sporcic and Knuckey 1998) has been produced to help in this respect and provide details on all operational aspects of the ISMP. This is an ongoing, dynamic process, however, and each year all ISMP staff meet to discuss these issues and incorporate required changes in their operational procedures.
Under Section 3(e) of the Fisheries Management Act 1991 (Commonwealth), AFMA is required to recover the costs of managing fisheries under Commonwealth jurisdiction from the fishing industry. In order to determine which management costs were to be recovered from the industry, the government established a task force in 1992. This task force examined, on a case-by-case basis, the reason why the service was provided, the type of service and the beneficiaries of the particular programme, and finally, it assessed whether or not the cost of the service should be recovered from one or more beneficiaries.
The evolution of recovering costs from industry for the ISMP was closely aligned with the evolution of the programme itself. When at-sea scientific monitoring by BRS and NSWFRI first began, projects were fully funded by the agencies together with funds from the Fisheries Research and Development Corporation, the Fisheries Resources Research Fund, or both. When these two projects finished in 1995, AFMA acknowledged the continued need for at-sea biological data collection and provided Commonwealth government funds for a subsequent 12 months while the design work was commissioned and operational requirements for a new integrated programme were developed. Funding for the ageing of SEF species by the CAF was from Industry levies. By 1 January 1997, the design and operational issues had not been completely resolved, but AFMA was required to review the provision of 100% government funding for the programme.
Because the ISMP collects valuable information, which is not available from any other source, for both stock assessment and wider environmental or ecosystem purposes, AFMA began recovering 50% of the cost of the ISMP from industry. This scheme began in January 1997 and will continue until 30 June 2000. Meanwhile, a review of cost recovery in relation to AFMA's involvement in research and scientific monitoring programmes will be conducted. When the results of the review are finalised, different cost recovery arrangements may apply to the ISMP in the SEF.
Although the ISMP presently covers only the trawl component of the SEF, a pilot study is underway to collect similar data on the non-trawl sectors. Appropriate sampling of the non-trawl sectors will be determined and is likely to be included in the ISMP. Many non-trawl vessels are also involved in the Commonwealth southern shark fishery, which will be implementing an ITQ system during 1999. The ISMP may become an important component in the data collection regime from this fishery in the future.
In addition to biological information used in stock assessments, the ISMP provides important data on fishing practices, bycatch and ecological interactions with non-target species. This aspect of the ISMP is becoming more important as the focus of environmental groups turns increasingly to the potential impacts of fishing on the marine environment.
In December 1998, the Commonwealth government released Australia's Oceans Policy (Anon, 1998) which outlined major new policy directions for maintaining the health and integrity of Australia's marine ecosystems. Important components of the policy relevant to the future direction of the ISMP include the assessment of the resources of large marine ecosystems for the purposes of integrated ocean planning and management.
In addition to the Oceans Policy, the following sections of Commonwealth legislation are becoming more important to fisheries managers:
- Endangered Species Protection Act 1992 (Commonwealth): A species can be listed as endangered or vulnerable (or other categories under the Act), in which case the process by which it is taken may be listed as a "key threatening process". This has occurred for turtles in the prawn-trawling fishery in northern Australia and has resulting in a recovery plan which is required under the Act, and for seabirds (mainly albatross spp.) in the tuna long-lining fishery, resulting in a threat abatement plan, also required under the Act.
- Wildlife Protection (Regulation of Exports and Imports) Act 1982 (Commonwealth): Schedule 4 lists species for which Environment Australia must issue a permit before export can occur. The Syngnathidae (seahorses, pipefish and seadragons), which can be taken as bycatch in trawling operations, are an example of such a group where permits of this nature are required.
The ISMP obviously plays a vital role in gathering this type of catch information. With the rising importance of domestic environmental legislation with respect to fisheries, it is important that the objectives, design and outcomes of the ISMP are reviewed as part of a dynamic process to ensure that the ISMP continues to make a significant contribution to fisheries management in the future.
The authors wish to thank Terry Walker (MAFRI) for useful comments on the manuscript and John Garvey (BRS) for valuable input about the organisation of the SMP.
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The integration of information collected by fishery observers into the fisheries management process: A scientific perspective
David W. Kulka
Department of Fisheries and Oceans, P.O. Box 5667, St. John's NF, Canada A1C 5X1.
Abstract: Three case studies are used to illustrate the value of fishery observer data in the scientific management of commercial fisheries;
- Discards in the Canadian Atlantic shrimp fisheries. Information collected by observers was used to quantify the discard of groundfish species in the Newfoundland, Labrador and Davis Strait shrimp fisheries. This study illustrates how observer data was used in co-operation with industry to refine fishing and management strategies.
- Distribution of northern cod. Catch and effort data collected from the northern cod fishery integrated with research data were used to define population shifts and fishing effort changes during the last years of the fishery. This analysis helped to clarify mechanisms that affected the collapse of the stock.
- Emerging fishery for skate. The distribution of fishing effort for a new target species is examined in relation to the distribution of the stock. In the absence of data on fish size in catches, the fishing locations are compared with skate distributions derived from research surveys to determine the part of the population being exploited.
Effective scientific management of marine fishery resources depends on the availability of detailed and reliable catch, fishing effort, biological and technological data. This implies a monitoring programme or programmes that can yield accurate and detailed information pertaining to all aspects of the fishing operations. The only monitoring system that can comprehensively meet these requirements is an observer programme. Qualified individuals deployed to the fleet to observe and record can collect any or all, scientific, regulatory and technical data information on fishing activity as required by fisheries managers.
Prior to the existence of observer programmes, commercial catch and fishing effort data were obtained only from logs recorded by vessel captains plus information collected at the point of landing (e.g. documentation relating to the sale or purchase of the catch). Data on size and age were also collected from fish landed in processing plants. These sources of information were generally unreliable and catch data were often under-recorded or not recorded at all for a portion of the fleet. Bycatch and discarded components of the catch were routinely under-reported. These sources were, in consequence, limited in scope, detail and accuracy, particularly with regard to the reporting of bycatch, discards and the location of the catch. Conversely, observers are able to provide comprehensive catch data for use in the management of stocks provided that coverage of the fleet is adequate. This source of information gives a first hand view of the commercial fishing activity in a form available from no other source.
In the assessment of the status of commercial resources, fisheries managers integrate data from a number of sources, particularly, research vessel surveys, landings reported by fishers, samples taken in fish plants and data collected by observers at sea. Scientific data on lengths and age of target species and the catch per unit effort, collected by observers are routinely integrated into stock assessment models. Additionally, because observations of the catch collected by fishery observers are recorded for each deployment of the gear and are precisely geo-referenced, the information can also be used to conduct research on the biology and distribution of exploited species and their fisheries.
This paper details three case studies which focus on such distributional analyses based on catch data collected by fisheries observers in the Newfoundland Region of Fisheries and Oceans, Canada. The case studies are presented to illustrate the value of information collected by fishery observers in the understanding of the biological status of exploited stocks. The examples given integrate observer data with other sources of monitoring information such as research surveys, to facilitate more comprehensive analyses. The results of such work not only facilitate inferences about biology and distribution of exploited species but can often be used in the creation of policy and to support management decisions that provide for improved conservation of the stocks.
Since 1977, two species of shrimp, Pandalus borealis and P. montagui have been fished in six management units off Newfoundland, Labrador and north into Davis Strait (Parsons and Veitch 1997 and Fig. 1) in what has become a growing and lucrative fishery over the years.
As the rather extensive northern shrimp populations overlap with the distribution of many groundfish species (Kulka 1995) the bycatch of fish species, in common with shrimp fisheries around the world (i.e. Maharaj and Recsiek 1991), is a common occurrence. The juveniles of these overlapping groundfish populations are particularly vulnerable to being inadvertently captured by the small mesh trawls used to exploit the shrimp. Comprising about 125 species in Canadian Atlantic waters, this bycatch is of no commercial value and is also a hindrance in the processing of the shrimp. All bycatch is therefore discarded causing significant mortality and particular conservation concern regarding the pre-recruits, of commercially valuable species.
Fishery observers have been deployed on the Canadian Atlantic shrimp fleet since 1980. The data gathered for this study, which was carried out by the DFO in co-operation with the industry (Canadian Association of Prawn Producers) and available from no other source, was used to examine bycatch in shrimp catches (Kulka and Firth 1987).
In addition to the quantification of all bycatch species and the determination of the size and age of the commercial bycatch (Kulka 1995, Kulka 1997), a spatial analysis was employed to define the areas of overlap of groundfish with shrimp populations. The study identified locations where bycatch was persistently high and also defined the best shrimp grounds (high shrimp catch rates in combination with low groundfish bycatch). For the period 1987 to 1995, a spatial overlay of shrimp catches with the most commonly caught commercial groundfish species in the discarded bycatch (i.e. redfish, Sebastes sp.; turbot Reinhardtius hippoglossoides; cod, Gadus morhua and American plaice, Hippoglossoides platessoides) was mapped over all shrimp grounds. Within the period of this study, a bycatch excluding device, the Nordmore grate, was first trialed and subsequently mandated based in part, on the results of this study.
Figure 1. Observed gear deployment locations (·) for the northern shrimp fishery for the period 1988 to 1994 and the location of shrimp management area 6.
The example presented here, extracted from the greater analysis that covered all shrimp management areas (Fig. 1) over 8 years, is used to illustrate the results of this greater body of work. Relatively high levels of bycatch were experienced in 1988 in the southern shrimp area 6 (Northeast Newfoundland Shelf), typical of the years prior the early 1990's (Fig. 2). Over nearly all of the area 6 grounds in 1988, the combined bycatch of commercial species exceeded 300 kg per day, a rate deemed excessive by industry and DFO. Less than 5% of the area fished yielded good (> 0.6 t per hour) shrimp catches in combination with low bycatch rates.
Based on these observed distributional patterns, which were relatively similar across all shrimp grounds, managers were able to arrive at a management strategy that effectively reduced bycatch in the shrimp fishery. Initially in 1993, a series of sub-areas were defined where the employment of a fish excluding attachment, the Nordmore grate, was made mandatory. These grate employment sub-areas corresponded to fishing grounds where bycatch of commercial groundfish was shown to be high (consistently in excess of 300 kg per day) from this study.
In 1994, grate usage was made mandatory in the southern shrimp management areas and eventually in 1997, the grate was made mandatory in all areas. This measure had a significant effect on bycatch and shrimp catch rates for area 6 in the first year of introduction (1994) greatly reducing the bycatch and also facilitating a shift in the shrimp grounds toward the shelf edge (Fig. 3). Bycatch was reduced to levels considerably less than 300 kg per day and shrimp catches exceeded 0.6 t per hour over about 85% of the fishing grounds.
Observer data recorded over this period showed that a combination of a change in fishing behaviour (a shift of fishing effort) and the introduction of the Nordmore grate led to a reduction in the bycatch of juvenile groundfish to very low levels. A decline in the abundance of groundfish stocks and an increase in shrimp also contributed to the observed changes. Bycatch was reduced from a peak of approximately 2,500 t of redfish, turbot, cod and American plaice in 1988 in area 6, bycatch to 200 t or less after 1993. Bycatch amounts continued to increase for the more northerly shrimp grounds until 1992 due primarily to catches of small redfish. Redfish taken from the Davis Strait were similar in size of the shrimp and observer records showed that substantial numbers slipped through the bars of the grates. Reduction in grate size in recent years and perhaps a reduction in the density of redfish concentrations have consequently resulted in a substantial decline in the bycatch in these northern areas since 1992.
In summary, detailed spatial data collected by fishery observers made it possible to:
- Delineate areas of high bycatch used to define sub-areas where the use of the Nordmore grate was required;
- Examine the effect of the grate on groundfish bycatch; and
- Make informed decisions regarding management of the bycatch problem.
The effect was a dramatic reduction in the bycatch from the northern shrimp fishery.
|Figure 2. Composite overlay of combined commercial bycatch rate with catch rate of shrimp in shrimp management area 6, 1988. Legend, shrimp vs. combined bycatch describes the different gray shades.||Figure 3. Composite overlay of combined commercial bycatch rate with catch rate of shrimp in shrimp management area 6, 1994. Legend, shrimp vs. combined bycatch describes the different gray shades.|
|Figure 4. Labrador and Northeast Newfoundland Shelves and northern section of the Grand Bank comprising the extent of the northern cod stock. The boxes depict the four areas discussed in the text.|
Northern cod (Gadus morhua), occupying the Northeast Newfoundland and Labrador Shelf (Fig. 4) underwent distributional changes starting in the late 1970's. These changes were concurrent with substantial population reductions culminating in a commercial collapse of the stock in the early 1990's (Kulka 1998a, Lilly et al. 1998). This study illustrates distributional changes in northern cod distribution in the years leading up to the collapse using detailed geo-referenced data from observer, research trawl and acoustic survey sources. Observers were deployed on 100% of vessels in the winter offshore fishery after 1986, allowing a detailed description of this fishery to be recorded.
Analysis of spatial patterns of the distribution and density of cod showed that the stock had undergone several major changes during the 1980's and 1990's (Kulka 1998b). During the autumn (research survey data), winter (fishery observer data) and spring (acoustic research data) in the 1980's, cod were found to be aggregated in four areas: North, along the Labrador coast from 51º00'N to the shelf edge north of 54º30'N; Middle, along the shelf edge between 51º30'N and 53º00'N; South, along the north-east slope of the Grand Bank to 50º30'N and; Grand Bank, on the top of the northern portion of the bank. (Kulka 1998a).
Analysis of autumn survey data revealed a relationship between the extent of the cod migration along the shelf edge and the distance inshore that these concentrations extended. Winter observer data complimented these observations, recording a non-migrational period when cod were aggregated along the shelf edge to spawn.
After 1985, the pattern of four locations of spawning aggregations started to change as the northern concentration started to diminish. This was the largest concentration during the years 1983 to 1988 (Kulka 1998a) and was the first to disappear during the collapse of the stock. (Fig 5a, Fig. 5b). From 1988 to 1990, the middle and southern concentrations first increased in terms of the extent of high-density areas and stock biomass, then rapidly declined until only a small remnant of the southern concentration remained in 1993. During 1989 to 1991, the remaining cod hyper-aggregated in the southern area (Rose and Kulka 1999).
The north to south pattern of the disappearance of the cod concentrations did not correspond with the distribution of fishing effort offshore. Based on the 100% observer coverage of fishing vessels targeting the stocks, fishing effort was observed to be consistently highest on the more southerly grounds over the period of decline (Kulka 1998a). This suggests that offshore fishing pressure inside 200 miles was not the primary cause of the distributional changes. Conversely, no clear relationship between environmental conditions and cod abundance, or distribution has been established. Although the distributional changes that were observed during the collapse of the stock are well defined and are based on observer information in conjunction with data from other monitoring programmes, the underlying reasons for the population collapse remains unclear.
With the decline of many fisheries world-wide, attention has turned to the exploitation of "non-traditional" species such as elasmobranchs (Hueter 1998). One example of such an emerging fishery is that for skates (Raja sp.) in Canadian Atlantic waters (Kulka and Mowbray 1998, Simon and Frank 1996).
Figure 5a. Distribution of the northern cod, 1988-1991. Upper panels show the autumn (fall) distribution based on research survey data. Middle panels show the winter distribution based on observer data and the lower panels show the spring distribution based on acoustic surveys. Lines depict acoustic tracks. Darker shades of gray denote more dense area of cod for all panels.
Figure 5b. Distribution of the northern cod, 1991-1994. Upper panels show the autumn (fall) distribution based on research survey data. Middle panels show the winter distribution based on observer data and lower panels show the spring distribution based on acoustic surveys. Lines depict acoustic tracks. Darker shades of gray denote more dense area of cod for all panels.
Previously, skate were known to be a common bycatch in many Grand Bank ground fisheries (Kulka 1982, 1984, 1985, 1986a, 1986b) but most were discarded. Exploratory work on the Grand Bank in 1993-1994 and the establishment of markets led to a regulated fishery by Canada inside 200 miles starting in 1995 (Anon. 1994, Day 1991). A non-regulated fishery by Spain successfully prosecuted since the late 1980's outside Canada's 200 N.M. limit (Junquera and Paz 1998) also suggested a market potential for this resource. The development of the Canadian skate fishery was in part the result of moratoria imposed on traditional groundfish fisheries coupled with the recognition that skate were marketable. Concentrations appeared sufficient to support a viable fishery (Atkinson 1995, Kulka et al. 1996, Kulka and Mowbray 1998, Mowbray and Kulka 1999).
Given that this was an emerging fishery, observers were deployed to a portion of the Canadian fleet during the exploratory phase which began in 1993. In total, approximately 8% of the fishing activity was observed over the life of the fishery (1993 to 1998) and in spite of these low observer coverage levels, the data proved useful in describing the spatial dimensions of the fishery. This was of particular importance in understanding the effect of fishing on the newly exploited resource. Regardless of gear used to catch the skate (Figs. 6a-c), all of the domestic activity occurred in a narrow band about 50 km long along the shelf edge centred near the dividing line between NAFO (Northwest Atlantic Fisheries Organisation) statistical Divisions 3O and subdivision 3Ps. The foreign otter trawl effort, based not on observer records but on data collected during surveillance boardings occurred on a completely different ground outside 200 miles on the tail of the Grand Bank in shallow water.
Canadian otter trawl effort on skates took place primarily along the south-western edge of the Grand Banks. Although most of the reported catches were from the spring (March to June as opposed to the foreign activity on the tail mostly after May), otter trawl catch rates as recorded by fishery observers at 730 kg per hour were about the same during both the spring and autumn (Kulka and Mowbray 1998). Longliner activity was more widespread in the spring and catch rates were generally lower at 180 kg per 1000 hooks. The best catches were achieved at the mouth of Haddock Channel in the autumn and some skate were also taken at the mouth of St. Mary's bay. Gillnet catches, primarily from NAFO statistical division 3O in the spring were highest near the 3O/3Ps border. Catch rates for this gear type averaged 2,500 kg per 100 nets. All gears in these areas were deployed in a fairly narrow range of depths, averaging 140 m. Both spring and autumn research surveys indicated that the skate along the south-western edge of the bank (where they were fished by Canada) were more densely aggregated at depths greater than that fished (Kulka and Mowbray 1998). The density of skate in the spring was lowest between 100 m and 200 m and peaked at depths of between 700 m and 800 m. Gear limitations may have effectively restricted effort to shallower waters.
Skate catch rates from research survey tows were superimposed on commercial otter trawl fishing grounds (Fig. 7). This analysis was conducted only for otter trawls since research surveys employed similar gear. It was determined that a mean weight per tow of approximately 30 kg (120 kg hr-1) during surveys on commercial grounds corresponded with commercial catch rates which averaged between 700 kg hr-1 and 800 kg hr-1. This suggested that the commercial trawls were about 6.25 times more efficient than Campelen survey gear for catching skate. The research vessel density plots were then re-scaled to show only areas with commercial potential (i.e. where catch per tow was greater than 15 kg, equivalent to a commercial catch greater than 325 kg hr-1 which is close to the lower limit of the range of acceptable catch rates). The result of this analysis was a plot of potentially commercial areas for skate.
Fisheries observer data combined with enforcement (inspections of foreign vessels) and research survey data were used to compare actual fishing effort (observer data) with the resource distributions estimated by research surveys. Commercial fishing positions (Fig. 7) superimposed on survey determined skate distributions showed agreement between actual and potential fishing areas. The observed fishing grounds covered 16,000 km2 and were approximately a third of the potential area of the fishery (circa 45,000 km2). In NAFO Div. 3Ps, Canadian activity corresponded with the areas of highest concentration although high concentrations along the edge of the Laurentian Channel just north of the fishing grounds were not observed to be fished. On the other hand, Canadian activity did not match with the areas of highest concentration in Div. 3O. The fishery in this area was concentrated near the 3O/3Ps border while the densest spring (and autumn) concentrations of skate were located approximately 150 km to 200 km further east. Conversely, autumn foreign fishing effort locations outside 200 miles in Div. 3N corresponded closely with the distribution of skate in the autumn and foreign fishing grounds overlapped almost entirely with the distribution of skate.
|Figure 6. Observed location of directed fishing effort on skate for the period 1993-1998, (a) otter trawl, (b) gillnet and (c) longline. Darker shades of gray depict areas with higher catch rates.||Figure 7. High-density areas of thorny skate (weight (kg) per tow) determined from research vessel survey data using Campelen trawls from 1995 to 1997. Areas shown are of sufficient density to support commercial fishing. Darker shades of gray depict higher densities of skate. Overlaid crosses depict commercial fishing locations.|
By relating observer data to research vessel data, it therefore appears that the Canadian commercial fishing effort is concentrated over a relatively small proportion of the potential skate grounds while foreign effort outside the 200 N.M. limit covers most available grounds.
The observer database is a valuable resource for fisheries managers and contains data on all aspects of fishing operations. Various types of data (e.g. measurements of fish lengths caught) are used as standard input for stock assessments. Observer data stands out from other sources of commercial fisheries data in terms of detail and accuracy and also has the distinct advantage of being geo-referenced allowing the types of analyses presented to be made possible. This paper illustrates how observer data combined with data from other (scientific) monitoring programmes, are particularly useful for describing distributions of both fish and the fisheries. This information in turn can assist managers of fisheries in making informed policy decisions.
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