The unit stock is a concept of fisheries biology that has its practical application in the treatment of data from fisheries. In stock assessment work we must know which data may be grouped together because they refer to individuals with a similar life pattern. To enable us to do this we describe each fish as belonging to its own unit stock.
A unit stock can be theoretically described as a group of individuals of the same species whose gains by immigration and whose losses by emigration, if any, are negligible in relation to the rates of growth and mortality. A unit stock is essentially a self-contained population with its own spawning area. It is isolated and fishing upon one unit stock has no effect upon the individuals of other stocks.
One unit stock which conforms almost completely with this definition is that of the Aroto-Norwegian cod. This spawns inside the Lofoten Islands, northern Norway; the eggs and fry are carried in the North Atlantic drift to Spitzbergen and into the Barents Sea, both of the areas forming the nursery grounds. Eventually the cod mature at 7 years and older when they return to the Lofoten Islands to spawn. There is very little emigration from the stock and no evidence whatsoever of immigration.
The cod stock at Iceland is similar except that probably some of the eggs spawned at Iceland drift to the extreme south-west corner of Greenland and, in some years, there is a return migration of mature cod to spawn at Iceland. Both the Icelandic and southern Greenland cod stocks are treated as separate stocks for assessment purposes, but the theoretical concept of complete isolation is no longer true.
The concept is further blurred in the case of the North Sea herring, of which there are three distinct populations, Downs, Dogger and Buchan. They have separate spawning grounds but intermingle on the feeding grounds at certain times of the year. These three herring stocks cannot be treated as unit stocks because the fishing mortality is common during that part of the year when they are mixed but, insofar as possible, data for three populations are collected separately and the populations assessed separately.
The North Sea cod presents the furthest departure from the concept of a unit stock. It is distributed all over the North Sea, but tagging experiments have indicated that the mixing of juvenile and adult fish from different spawning grounds is a very slow process, which can be illustrated by a series of overlapping circles. Fig. 8.1.
Fig. 8.1 Overlapping circles representing North Sea cod populations, each based on a spawning area
Cod from one spawning area mix with those spawned in an adjacent area and the one next to that, but individuals at the opposite ends of the areas will probably never mix. Consequently, exploitation of the cod in one part of the North Sea will not affect the whole population in the same way.
Neither the individual populations derived from a single spawning nor the whole set of populations can be considered as falling within the definition of a unit stock, although it is practical to assess the North Sea cod as two unit stocks.
All these examples are taken from the North Atlantic but similar variations in the degree of separateness exist elsewhere. In Lake Mobutu Sesseseku (Albert) at least two populations of Alestes baremose exist, one at the north and one at the south end of the lake, based upon spawning grounds in the rivers Nile and Semliki respectively. Distance prevents fish of the two populations mixing and they form two unit stocks, even though they are biologically and probably genetically inseparable. Non-migratory fish in rivers probably form a similar parallel to cod in the North Sea.
Thus, although the term ‘unit stock’ has a strict definition its practical application depends upon the extent to which individuals of a stock can be identified. With increasing knowledge of a ‘unit stock’ it may be possible to divide it into two or more ‘unit stocks’, as is happening with North Sea cod. Originally assessed as a separate stock it is now being assessed on the basis of a northern and a southern stock.
Individual members of the unit stock are rarely sedentary and a knowledge of the migration of fish species is most important and useful when dealing with their biology and dynamics since the distribution of the effort of the commercial fishery may be closely related to the pattern of migration of the species concerned.
Nikolsky (1963) defines migration of fishes as an active, but occasionally passive, main movement from one habitat to another, and Heape (1931) as a class of movements which impels migrants to return to the region from which they have migrated. Jones (1968) remarks that the word ‘impels’ is used in the sense of biological necessity.
Both Heape (1973) and Nikolsky (1963) note three main movements in the migratory cycle of fishes:
Nikolsky (1963) mentions that the reason why some fish species migrate is that there is not enough food for both the adult and the young parts of a large population to live in the same area. They have to either increase their feeding areas or restrict their abundance.
Jones (1968) discusses Nikolsky's work and theories and mentions that if migration is an adaptation to abundance it would explain why the important commercial species are migratory; they are of commercial interest because they are abundant and abundant because they are migratory.
The current can be considered as the mechanism into which the unit stock is locked, holding its members together to form that unit stock, and patterns of migration are described in terms of these currents. Pelagic eggs and larvae drift with the current (a denatant movement) to the nursery area (a feeding migration) and the adult individuals swim against the current (a contranatant movement) back to the spawning area (spawning migration) as shown in Fig. 8.2.
(Feeding wintering) Adult stock
Some marine fish, such as herring, and the majority of freshwater fishes do not have pelagic eggs but fix them to plants or the substratum. Some species notably the cichlids are mouth brooders. This is not only an adaptation which provides the eggs and fry with parental protection but also enables the species which occur in rivers to spawn without migrating up-stream as do the majority of riverine fish. During the time from spawning and until the hatched larvae are able to withstand the current the larvae may be carried very long distances away from the spawning area. Therefore, a spawning area must be in such a position in relation to the direction of the currents that the larvae and young fish are carried to nursery areas where suitable feeding conditions exist. The spawning migrations of adult fish are normally an active migration against the current (contranatant) to compensate for this.
If the main currents in the sea are principally responsible for the migration of fish it could help to explain the absence in the tropical zone of species which perform regular long-distance migrations. Cushing (1959) mentions that in the tropical zone the environmental conditions can always be favourable for the development and survival of eggs and larvae at all times of the year and in all localities covered by an inter-tropical gyral.
In the temperate or arctic zones, where food is not available in more or less equal quantities throughout the year, production cycles differ from those in the tropics. Thus, if the young are to survive in these zones the adult fish have to spawn in the right place and at the right time. It follows from this that in the temperate and arctic zones there must be an annual cycle of activity in the gonads.
The following terms and definitions of fish migrations proposed by Meyer (1949) have been generally adopted:
Truly migratory fishes which migrate between the sea and freshwater.
Diadromous fishes which spend most of their lives in the sea and migrate to freshwater to breed (salmon, sea trout, shad, sea lampreys, sturgeons).
Diadromous fishes which spend most of their lives in freshwater and migrate to the sea to breed (eel, Salangidae, Galaxidae, Retropinnidae).
Diadromous fishes which migrate from the sea to freshwater or vice versa, but not for the purpose of breeding (some Exocidae, Perca fluviatilis, some Mugilidae).
Truly migratory fishes the migrations of which occur wholly within freshwater (trout, bream, Coregonoids).
Truly migratory fishes which live and migrate wholly in the sea (cod, herring, capelin, tuna, mackerel).
This should, in fact, be termed ‘methods of tracing fish migrations’ because attempts to explain them in real terms are rather more difficult. There are numerous methods for tracing the migrations of fishes.
It is not possible to fit successfully tags to all fish species and all size groups of fish. In such cases the fish may be marked by fin clipping. Fig. 8.3 shows some combinations of fin clipping which have been used. If possible some fish should be kept in captivity to determine how long it takes the fish to re-generate. This can be a matter of weeks in tropical conditions. Adipose fins do not regenerate. Similar problems are experienced with crustaceans like lobsters, because these animals cast their shells during moulting. Clipping of the telson as shown in Fig. 8.4 should be satisfactory and still visible at least after two moultings.
Small fish can also be marked by injecting liquid latex and colour coding allows a limited amount of differentiation between groups of marked individuals (Riley, 1966). These methods are only satisfactory if the total number of lobsters or fish landed is relatively small and they can be handled and examined individually.
A large number of different devices have been used for tagging fish and shellfish. In the Journal du Conseil (ICES, 1965) about one hundred tags are figured and briefly described. Numerous papers have been written on the subject, which it is impossible to cover in detail here. Only the main types of tag and tagging methods will be described.
Any fish tag should be as small as possible so as to cause least interference with the normal behaviour of the fish. External tags should not be so conspicuous that they make the fish more vulnerable to predation but must be easily visible to the potential finder, two conflicting requirements which are usually solved in favour of the latter. They must be cheap and easy to make because many thousands are usually required and, if possible, they should be entirely machine made to minimize demands on manpower. Each should have a number which uniquely identifies the fish to which it is attached.
Internal tags are used on fish, such as herring, anchovy and whiting which are landed in large quantities for reduction to meal and oil. They are not handled individually and the chance of an external tag being noticed are very small. Internal tags are small steel plates with identifying letters and numbers (Fig. 8.5). They are put, or shot, into the body cavity with a pair of pincers or a gun (Fridriksson and Ansen, 1962; Ansen et al., 1961). In order to remove pieces of iron, which may have been accidentally dropped amongst the fish, strong magnetic separators are fitted to the conveyor belts carrying the fish into the factory. The steel tags also collect on these. During the period August 1969—March 1970, 58,000 young herring were tagged in this way in the North Sea.
Internal tags are also used on prawns and shrimps which are also landed in large numbers but which are individually handled in processing. These tags are plastic and are inserted laterally into the musculature of the first abdominal segment (Fig. 8.6).
The majority of tags in use are external tags of which only a limited number will be described:
1. The Petersen disc (Fig. 8.7)
The Petersen disc has been one of the most successfully and widely used tags in the history of fisheries biology. It consists of two plastic buttons which are attached one on each side of the fish with a pin made from either titanium or stainless steel wire; silver wire used to be used but it becomes brittle after one year and tag shedding results. The method of making the wires and attaching the tag are shown in Fig. 8.7. As the wire is bought in reels the pins have to be cut; if alternate cuts with wire cutters are made at 45° a point is formed on two consecutive pins with one cut. These points are very sharp and care should be taken in handling pins.
One of the discs carries an identification number and letter or letters. Within ICES member nations the latter are internationally-agreed so that details of recaptured fish can be returned to the country of origin irrespective of where they are caught.
On flatfish, such as plaice, the tag is fitted just below the dorsal fin (Fig. 8.7); on rays it is fitted on one of the pectoral fins midway between the gill slits and the apex of the fin. On roundfish it is also fitted below the dorsal fin. It should not be fitted to bony structure such as the operculum because the wire erodes the bone and the tag is quickly lost. When the fish is tagged the discs should be loose on the wire, with up to 5 mm slack depending upon the size of the fish, to allow for growth.
2. The Lea tag (Fig. 8.8)
The Lea tag is a cylinder of plastic containing a message, number and letter code printed on paper. Usually the cylinder is yellow in the central part and blue at the ends. This tag is termed ‘hydrostatic’ because it is neutrally buoyant in water. It is used exclusively on round fish and is normally fitted to the fish in front of the (first) dorsal fin, preferably with a soft-braided nylon; bridle; those of wire or monofilament nylon cut the fish flesh, causing wounds and eventually shedding of the tag. The bridle is sewn through the fish using a curved surgical needle with a split eye into and out of which the bridle can be easily slipped (Fig. 8.9). This tag has been used mainly on herring, mackerel and cod.
3. The plastic flag tag (Fig. 8.9)
Because the Lea tag has to be assembled by hand, it has largely been replaced by the flag tag, made from sheet polythene. These are stamped indelibly with a message and the number written on with special insoluble ink. The size of the flag can be designed to suit the size of fish being tagged. Until recently it was possible to obtain these flags with a mercury salt incorporated in the plastic which eliminated fouling. However, restrictions on the use of mercury and difficulties in printing on the impregnated plastic have resulted in supplies of this type being discontinued. The flag tag is attached with a soft braided nylon bridle, as the Lea tag. (Fig. 8.9).
4. The spaghetti tag
The spaghetti tag (Fig. 8) is a length of yellow polythene plastic tubing, 20–30 cm long with an external diameter of 0.10–0.35 cm. Instructions to the finder are either printed directly on the tube or on a red plastic label fitted inside it. The tube is sewn through the back of the fish using a curved surgical needle, whose blunt end is designed to fit into the tube leaving its outside flush with that of the needle (Fig. 8.11). The spaghetti tag has the advantage that it does not need a separate bridle. Their disadvantage is that it is difficult to get the needles to match the tags, which often slip off during insertion.
Recently manufactured plastic flags which have no bridle and which can be inserted with a gun have become available (Rauck, 1969). This method of application is very quick and the results obtained appear to be as satisfactory as obtained using older methods.
5. Plate tags
In Scotland, for salmon smolts, a pair of small plastic or stainless steel plates 30 mm by 6 mm is used. These plates are fastened one each side of the base of the dorsal fin with wire, which passes through holes at each end of the plates. The tags are meant for recovery when the fish has returned to freshwater after life in the sea. During this period the flesh covers the tag so to identify the tagged fish, most of which are individually handled, the adipose fin is removed at the same time as the smolts are tagged.
6. Tags used on molluscs
Molluscs have been tagged in two ways. One method is to slightly grind the shell to give a dry, smooth surface and then attach a numbered Petersen with waterproof glue (Thomson, 1963). The other method, suitable for scallops, is to drill a hole through the anterior ear of the flat valve with a power drill and attach a numbered Petersen disc with stainless steel wire (Rolfe and Franklin, 1973).
7. Tags used on crustaceans
Crustacea have been tagged by wiring Petersen discs to their shells (Simpson, 1963) but these are lost at moulting. The suture tag has been used to overcome this problem with crabs; a piece of surgical wire is sewn through the epimeral line of the crab and onto this a numbered Petersen disc is threaded, the ends of the thread being sealed together with a lead seal (Mistakidis, 1959) (Fig. 8.12). Various methods have been used to tag decapod crustacea including small Petersen discs and dart and loop tags inserted at the junction of the cephalothorax and abdomen (Fig. 8.13). Neal (1969) reviews methods of making and tagging shrimps.
When planning a tagging experiment it is necessary to:
(a) select a tag which is suited for both the species and the commercial fishery concerned; for example, Petersen discs used on fish which are most likely to be caught in a gill net or stake net will make the fish more vulnerable to capture than untagged fish because the meshes will catch on the wire between the fish and the discs;
(b) choose a fishing gear which will not damage the fish when catching them;
(c) choose the right season of the year;
(d) choose the right depth for catching, if there is a choice; if the fish are in water deeper than about 40 m those species with closed swimbladders, like cod, haddock and hake, will often come up completely bloated because the process of reabsorbing the gas from the swimbladder is slow and the overpressure (1 atmosphere for every 10 m of water) leads to the swimbladder expanding;
(e) issue publicity to the fishermen about the tagging experiment;
(f) place all the tags, in order, in a secure fashion (on a piece of wire) so that they cannot be lost and have all other equipment carefully labelled and easy to hand;
(g) secure suitable facilities on board the ship: tank capacity, running water and measuring boards.
It is also necessary to have sufficient tags to tag that number of fish which will give a meaningful result. This means knowing something about the likely return rate. If possible a pilot scheme should be run first but this is not always possible.
To keep the fish in the best possible condition:
(a) use the gear which will cause them the least damage; purse-seines are best for pelagic fish if it is possible to catch them that way; bottom trawls should be rigged to catch the least possible amount of benthos and stones and the codend should be of soft material; Maucorps and Lefranc (1973) describe a canvas codend which minimizes water movement within it during towing and retains water on hauling.
(b) transfer the fish from the gear to the holding tanks as gently and as quicky as possible; these tanks should have a continuous supply of running water if possible; if not, the water should be renewed as often as possible with a bucket so as to keep it well oxygenated and its temperature near ambient;
(c) remove fish which are dead, swimming belly up or have visible damage;
(d) measure the fish and if possible record both the sex and the maturity. Record these details and any others needed against the number of the tag in a logbook;
(e) fit the tag to the fish as quickly as possible;
(f) liberate the fish and record the position of liberation. Normally this is recorded for each block of tagged fish released at that station. Fish with expanded swimbladders can be successfully released by putting them in a cage which can be opened at depth from the ship. The fish in the cage are lowered as deep as possible, the door of the cage opened and the cage retrieved.
The rate of returns from a tagging experiment is affected by:
(a) the fishing mortality rate;
(b) the natural mortality rate;
(c) death of fish caused by capture and tagging
(d) loss of tags.
The fishing and natural mortality rates are two parameters which can be measured from a well-conducted tagging experiment but the accuracy of their estimation will depend upon death of fish caused by tagging and loss of tags.
Death of fish due to capture and tagging can rarely be eliminated entirely. The stress of capture, which results in lactic acid accumulating in the blood, can be lethal and Bagge (1970) found that this factor was more important than any other. Strict regard to factors (a)-(b) described in section 220.127.116.11 will minimize death from this cause.
It is possible to get an estimate of this mortality by:
i) keeping the tagged fish in tanks or keepnets for some hours;
ii) using two different types of tags;
iii) classifying the individuals tagged according to behaviour in the tank before tagging and to visible damage (loss of scales, etc.).
Beverton and Bedford (1963) classified whiting which they were tagging by scale condition (good, moderate and poor) and by the way of swimming (floaters, swimming belly up in the tank, and sinkers, swimming lively around the bottom of the tank). The fish classified as “good - sinkers” yielded returns four to five times higher than “poor - floaters” and “poor - sinkers” respectively.
Death of fish can also be caused if the tag is either unsuitable and leads to rejection, or makes the fish more liable to predation or leads to the fish becoming entangled in plants or upon rough rocks.
Loss of tags is caused by either the fish shedding the tag or the tag not being returned after the fish carrying it has been recaptured. Loss of tags can be avoided by choosing a suitable form of attachment (titanium or stainless steel but not silver pins for Petersen discs, suture and not-wired-on tags for crabs, both mentioned previously). Losses can be checked by running a double tagging experiment either with two tags attached by different methods to the same fish or by tagging alternate fish with different tags. Fish can also be kept in aquaria to determine loss rates.
Loss of tags after the fish has been captured can be caused in many ways. The tag may not be easy to detect or it may carry insufficient instruction to the finder as to what he should do with it. The finder should get a reward which is large enough for him to make it worthwhile returning the tag and its level should be reviewed at annual intervals to make sure its relative value does not fall as other prices increase. If the fish is returned the value of the fish should be paid plus any other expenses.
In some countries premium awards are made. Not only does the finder get a reward but all the numbers of the tags returned over a given period are put into a lottery and the winner gets a very large prize with attendant publicity. This is better than having one tag for which there is a big prize because once it is known that this fish has been caught interest in looking for tags rapidly drops. These methods can be used only where gambling does not offend the fishermen's moral code.
The finder should be given information as to where the fish was tagged and what is the purpose of the experiment. International arrangements need to be made so that tags used by one country and returned to that of another are accepted, paid for and the information passed on. Tags may not be handed in for peculiar reasons; if the fishermen do not get on well with the fisheries biologist they will enjoy not returning his tags; sometimes fishermen will not return the tags of one nation whom they dislike for some reason; care must also be taken that the tags used do not have any symbolic or religious significance that might anger the fishermen.
Methods used in analyzing tagging experiments are given by Jones (1966).
By studying the distribution of the fishery on a species it is possible to gain some idea of changes in availability in different areas which may indicate migrations of the recruited stock. These data are particularly useful at spawning time when the mature part of a unit stock is likely to be separated from the mature part of any other unit stock.
By using echo-sounders it is possible to register fish schools whose species composition may be identified by repeated fishing. Repeated surveys may indicate the directions of movements of the fish concerned. More advanced echo-sounders (integrators) make it possible, by measuring the strength of individual signals, to estimate the size of the single fish and, in several cases, the species. The movements of the Atlanto-Scandinavian herring were traced in this way.
Studies of parasites as biological tags have given some promising results. Two parasites of the Pacific sockeye salmon, which inject it in freshwater, have been very useful in distinguishing the geographical origin of fish caught on the high seas; one is larval Triaenonphorus crassus, a cestode which occurs in the muscle and which predominates in fish of Alaakan Bristol Bay origin; the other is a nematode, Dacunitus truttae which is found in the muscle and occurs most commonly in industrialized of Asian origin. Scientists estimated the proportion of cod of Greenland origin in the spawning fishery at Iceland from the occurrence of larval codworm, Terranova decipiens which occurs only in cod of the Icelandic stock.
The protein fractions of animal tissue can be separated by passing a low voltage DC current through them. If this is done on a slide coated with a suitable agar gel the constituent amino acids travel through the gel at different speeds to form bands. The position of the bands has to be identified by staining (Fig. 8.14).
For fish most of this work has been based on the use of blood proteins such as gamma globulin. To date the technique has been used on post-larval fish and has shown differences only between widely separated unit stocks. However, the occurrence of the different protein fractions is determined genetically and the method is now being developed to enable the work to be extended to larvae. This offers the possibility of being able to follow larvae from a particular spawning ground into their nursery areas and to link spawning stock with recruits in a more direct manner than has hitherto been possible.
From the scales of diadromous fish like salmon and sea trout, which spawn in freshwater, it is possible to gain information on the main movements between freshwater and the sea. Salmon and sea trout stay in freshwater from 1 to 7 years after hatching. During that time their growth is slow and the rings laid down on their scales are close together. When the fish migrate to the sea, their growth increases enormously and the distance between the rings becomes broad. The two types of growth pattern are easy to distinguish. After staying 1 to 3 years in the sea the fish return to freshwater to spawn. The fish then stop eating and use their fat reserves to satisfy their energy demands when swimming up river against the current. This results in a spawning mark on the scales in the form of a ring somewhat different from the annual rings. If the salmon survive the spawning they return to the sea and start eating again and the distance between rings is again large. The number of years which juvenile salmon stay in freshwater varies between countries so the number of juvenile rings also indicates the country of origin. (See also section 18.104.22.168).
Meristic characteristics are those which are countable such as vertebrae, fin rays, scales and fecundity. Several authors have shown that there is a relationship between some meristic characters and the environmental conditions to which the eggs and larvae are exposed.
Schmidt (1921) showed that eggs of trout from the same parents, incubated at various temperatures, produced fry in which the average numbers of vertebrae were higher at both low and high temperatures (3° and 9°C). Taning (1944) confirmed Schmidt's results and also showed that the number of rays in the pectoral and the dorsal fins increased with temperature. Zijlstra (1958) combined all data on herring given so far on vertebra counts and the temperature on the spawning grounds, and demonstrated a clear negative correlation (Fig. 8.15).
The same result has been demonstrated experimentally by Hempel and Blaxter (1961) who also showed a generally positive correlation between salinity and myotome counts (Fig. 8.16).
Hempel and Blaxter (1967) also showed a relation between the individual egg weights of North East Atlantic herring and the spawning time (Fig. 8.17) which they explained as an ecological adaptation to environmental conditions. Evidence is also accumulating that meristic characters are also partly genetically determined. Thus, fish of similar genetical pattern (of the same stock) are likely always to spawn in the same area. The conditions in this area at spawning time are likely to be uniform from year to year because the eggs and larvae are less tolerant of a wide range of environmental conditions than the adults and therefore the adults must be adapted to return to the area where these conditions exist. In consequence the meristic characteristics will not change from year to year and they become diagnostic of the stock.
Individuals cannot be separated by their meristic characters but only populations by their differences in mean numbers. Also, it is usual to use two or more characteristics and to combine the data by means of mathematical techniques such as discriminatory functions and distance functions (Fischer, 1936 and Rao, 1962).
The meristic characters which have been or are currently in use for stock identification are as follows:
i) Vertebral number
ii) Keel scale number
iii) Fin ray number
iv) Gill-raker number
v) Body proportions
vi) Individual skeletal structures.
i) Spawning time and maturity stage
ii) Growth in the first year (more precisely the formation of the first winter scale ring; (see section 4.3)
iii) The overall pattern of growth.
By far the greatest attention has been paid to the morphological characters, vertebral number, keeled scale, number and body proportions and to physiological characters, spawning time, fecundity and growth.
One other characteristic that can be used for separating stocks which is not meristic is overall external appearance, such as shape and pigmentation.
Aasen O, et al., 1961 ICES herring tagging experiments in 1957 and 1958. Rapp.P.-V.Reun.Cons. Perm.Int.Explor.Mer., 152:43
Bagge, O., 1970 The reaction of plaice to transplantation and tagging. Medd.Danm.Fisk-og Havunders., 6(5):149–332
Beverton, R.J.H. and B.C. Bedford, 1963 The effect on the return rate of condition of fish when tagged. Spec.Publ.ICNAF., (4):106–16
Cushing, D.H., 1968 Fisheries biology. A study in population dynamics. Madison, Milwaukee, University of Wisconsin Press, 200 p.
Fischer, R.A., 1936 The use of multiple measurements in taxonomic problems. Ann.Eugen., 7:179–86
Fridriksson, A. and O. Aasen, 1952 The Norwegian-Icelandic herring tagging experiments. Report No. 2. Rit.Fiskideild., (1):54 p.
Heape, E., 1931 Emigration, migration and nomadism. Cambridge, Heffer, 369 p.
Hempel, G. and J.H.S. Blaxter, 1961 The experimental modifiction of meristic character in herring (Clupea harengus L.). J.Cons.Perm.Int.Explor.Mer, 26(3):336–46
Hempel, G., 1967 Egg weight in Atlantic herring (Clupea harengus L.). J.Cons.Perm.Int. Explor.Mer, 31(2):170–95
ICES, 1965 A guide to fish marks. J.Cons.Perm.Int.Explor.Mer, 30(1):89–160
Jones, F.R.H., 1968 Fish migration. London, Edward Arnold, 325 p.
Jones, R., 1966 Manual of methods for fish stock assessment. Part 4. Marking. FAO Fish.Tech. Pap., (51)Suppl.1:90 p.
Maucorps, A. and G. Lefranc, 1973 Dispositif expérimental permettant de capturer au chalet des poissons vivante. ICES, CM.1973/B.24
Meyer, G.S., 1949 Usage of anadromous, catadromous and allied terms for migratory fishes. Copeia, 1949:89–97
Mistakidis, M.N., 1959 Preliminary data on the increase in size on moulting of the edible crab, Cancer pagurus. ICES, CM.1959:Dec.52 3 p. (mimeo)
Neal, R.A., 1969 Methods of marking shrimp. FAO Fish.Rep., (57)Vol. 3:1149–65
Nikolskú, G.V. 1963 (L. Birkett, Transl.), Ecology of fishes. London, Academic Press, 352 p.
Rao, C.R., 1952 Advanced statistical methods in biometric research. New York, John Wiley and Sons,
Rauck, G., 1969 A simple way for tagging flatfish by means of a tagging gun. ICES, CM.Demersal Northern Committee. F16:2 p. (mimeo)
Riley, J.P., 1966 Liquid latex making technique for small fish. J.Cons.Perm.Int.Explor.Mer, (30):354–7
Rolfe, M.S. and A. Franklin, 1973 Tagging scallops (Pecten maximus) in the English Channel. ICES, CM.1973/K24
Schmidt, J., 1921 Numerical signification of fused vertebrae. C.R.Trav.Lab.Carlsb., 14(16):1–5
Simpson, A.C., 1963 Making crabs and lobsters for mortality and growth studies. Spec.Publ. ICNAF, (4):188–93
Toning, A.V., 1944 Experiments on mersitic and other characters in fisheries. 1. Medd.Komm Danm.Fisk.-og Havunders., 11(3):1–66
Thomson, J.M., 1963 The tagging and marking of marine animals in Australia. Spec.Publ.ICNAF, (4):50–8
Zijlstra, J.J., 1958 On the spawning communities of the herring of the southern North Sea and English Channel (preliminary results). Rapp.P.-V.Réun.Cons.Perm.Int.Explor. Mer, 143(2):134–45
|Fig. 8.3||Combinations of fin clipping used to mark salmon smolts at Cultus Lake, Fraser River, British columbia (after Foerster, 1937)|
|Fig. 8.4||Telson of lobster marked by clipping (after Poulsen, 1967)|
|Making Institution||Denmarks Fiskeri- og Havunderøgelser, Charlottenlund Slot, Charlottenlund.|
|Type||Internal tag made of stainless steel or nickel-plated iron.|
|(A) 20 × 4 × 1 mm. Stamped DA and a number, usually denoting a series of 50 tags.|
|Use||Whiting and Sandeel|
Placed in the abdominal cavity of the fish.
|Scale of Reward||Fish with full information ………… 10.00 D.kr.|
|Reception Office||Same as Marking Institution.|
Fig. 8.5 (After ICES, 1965)
Fig. 8.6(b) Method of insertion of internal polyvinyl chloride tags (from Neal 1969).
Fig. 8.6(b) Method of insertion of internal polyvinyl chloride tags (from Neal 1969).
Fig. 8.7 Petersen disc (after Bagge, 1970) Note enlargement of wire point)
Fig. 8.8 Lea tag with braided nylon thread
Fig. 8.9 Enlarged surgical needle showing the split eye (a) and fish tagged with a plastic flag tag (b)
|Marking Institution||Fisheries Research Board of Canada|
|Type||Spaghetti tag, yellow vinyl tubing stamped “ Reward-Return Fish, Res. Board, St. Andrews, N. B., S-(number)”.|
30 mm × 2 mm.
Tag attached to dorsal musculature below dorsal fin.
|Scale of Reward||For tag and information ………… 1·00 C. dollar.|
|Reception Office||Fisheries Research Board of Canada, St. Andrews, N.B.|
Fig. 8.10 Spaghetti tag (After ICES, 1965)
|Fig. 8.11||Enlarged end of needle used to insert spaghetti tags showing butt shaped to fit inside of tube, which is shown in cross section.|
Fig. 8.12 Crab fitted with suture tag (from Mistakidis, 1959)
Fig. 8.13 Shrimp marked with the peterson disc tag. (from Neal 1969)
|Fig. 8.14||Fig. 8.14 Slide showing stained bands after electrolysis of proteins through an agar gel: unknown belongs to same group as Control 1|
|Fig. 8.15||Relationship between mean number of vertebrae and
temperature on various spawning grounds (see text)|
= data from Le Gall, Runnström and wook.
= total 1952, 1953, 1954.
• = year–class means
|Fig. 8.16||The effect of incubation salinity on mean myotome count. (Hempel and Blaxter (1967))|
|Fig. 8.17||Relation between individual agg weight of various stocks of North- East Atlantic herring and month in which fish of each stock spawn.|