Selectivity of fishing gears used in the Baltic Sea cod fishery

Abstract

The Baltic cod (Gadus morhua) plays a very significant role in the Baltic Sea ecosystem being the major fish top predator and the most important commercial species for the Baltic Sea fishing industry. Consequently the management and understanding of the exploitation pattern of the stock is of major importance. Technical regulations, improving the selectivity of cod, have been a major management strategy and the Baltic Sea is likely to be the area where most fishing gear selectivity studies, focussing on size selectivity, have been conducted over time. The methodology for conducting and analysing selectivity data has been significantly improved in recent years. The subject is reviewed since the choice of methodology can have a significant effect on the interpretation of the outcome of selectivity experiments. Factors affecting the selectivity of trawl and gill nets are considered. Alternative ways to improve the size and species selectivity of trawls using selective devices are reviewed. Selectivity parameters from available literature are listed and the correlations of selectivity parameters to the mesh size for different gears are estimated. The historical legislation on selectivity is reviewed and the expected selectivity for trawls is estimated. Management considerations concerning the mortality of escaping and discarded fish and wider management impacts have to be considered if improving selectivity. The review is ended by conclusions including reflections on needed research in the future.

Factors affecting the fishing impact on cartilaginous fishes in southeastern Spain (western Mediterranean Sea)

“…Fishing has caused a general decline in fish biomass and placed many marine species under serious conservation concern (e.g. Casey and Myers 1998, Pauly et al 2002, Baum et al 2003, Dulvy et al 2003, Sadovy and Cheung 2003, Madsen 2007). According to a United Nations Food and Agriculture Organization (FAO) estimate, over 70% of the world's fish stocks are either fully exploited or depleted.…”

Quota implementation of the maximum sustainable yield for age-structured fisheries

“…These technologies are such that only mature fish can be harvested (juveniles cannot be harvested), and selecting for old mature fish or young mature fish may be perfect or imperfect. This type of selection is observed in some fisheries (Quaas et al 2013;Madsen 2007;Broadhurst and Millar 2011;Squires and Vestergaard 2013). The current analysis focuses on the situation in which both fleets target or try to select the old mature class since the market price of old mature fish is higher than the market price of young mature fish.…”

“…The fishing technology or the degree of selection for fleet ݅ is denoted as ݆ . This degree of selection for fishable age classes can depend on gear types used by fleets (Madsen 2007).…”

“…Moreover, Madsen (2007) estimates selectivity of fishing gears used in the Baltic Sea cod fishery and shows that the degree of precision for selecting specific age groups can be increased by using passive gear types. Perfect selectivity for the old mature fish cohort (݆ = 1 or ‫ݍ‬ ଵ = 0), is always possible in our environment if the mesh size is large enough.…”

Untitled

“…On the other hand, T90 codends, in which standard diamond mesh netting is turned 90° could potentially improve size selective properties compared with traditional codends made of the same netting. As standard conventional netting can be used, a T90 codend is a very simple way to potentially improve the size selectivity of the fishing gear (Madsen, 2007). T90 mesh codend was initially tested for determination of selectivity of cod (Moderhak, 1997) Bogue, (Boops boops Linnaeus, 1758) is a commercial species and living on all types of bottom, as well as semi-pelagic, and sometimes in coastal waters.…”