Assessments, using General Production models, were attempted for each statistical division.
For divisio 34.1.1 it appears that there has been a moderate reduction in both catch and effort since 1979 and 1981 when both catch and effort were at a maximum. One implication of this result is that catches could be increased by allowing effort to increase to the level estimated for 1979 and 1981. However, it was felt that this assessment should be interpreted with caution and that no further increases in effort should be permitted until a better assessment could be done.
For the division 34.1.2, no assessements were attempted due to inconsis tencies in the data and the possibility that some catches reported as having come from division 34.1.2 may habe come from other divisions.
For divisions 34.1.3 and 34.3.1 there are many different fleets and types of boat which catches per unit effort can be calculated to provide indices of abundances. For each division, it was found that the various sets of catches per unit effort gave inconsistent pictures of the changes in abundance. This was believed to be due to shortcomings in the statisti cal data (see section 2.2). Because of this it was felt that assessments for these divisions as a whole.
Within division 34.1.3 ther is a separate fishery by Canarian artisanal fishermen who fish for sparids as target species on untrawlable grounds. For this one fishery, it was concluded tha further increases in fishing effort could be associated with further increases in yield.
For some species for which the appropiate biological data were avaliable, yield per recruit assessments were also considered. Thirteen assessments were done for 12 species of sparids in division 34.1.3. For all but one of the assessments, it was concluded that as increase in mesh size and/or a decrease in fishing effort, should lead to increases in yield per recruit. One assessment was also done for one species of sparid (Pagellus bellottii) in division 34.3.1. It was concluded that an increase in yield per recruit and that fishing effort should not be allowed to increase as long as the exploitation strategy remains unchanged.
A major difficulty in using General Production models for assessing sparid stocks was due to shortcomings in the statistical data. For example:
There can be big differences between the official and non-official versions of the statistics.
There are many different kinds of vessels.
The fisheries are dispersed.
Ther can be uncertainties about the allocation of catch statistics to statistical divisions.
Species separation in the statistics is often incomplete.
Sparids are only by-catches in fisheries directed at other species groups, and often form only a small proportion of the total catch.
Estimates of discarding, where they have been made, indicates rela tively high rates of discarding of sparids.
The members of the Working Group took note of evidence (Caddy, 1981; Gulland and Garcia, 1984) that during the Sixties there was a decline in sparid catches associated with an increase in cephalopod, and particularly in octopus catches. The possibility of a “replacement” of sparids by cephalopods has been suggested by a number of authors, but the members of the Working Group were not able to add anything useful to this topic.