Abstract
The paper provides a broad overview of issues relevant to management of fisheries for juvenile fish in contrast to the many stock assessments following Beverton and Holt’s (1957) approach for rational exploitation of mature fishes. A perspective on assessing these fisheries is illustrated for juvenile European hake, Merluccius merluccius, in the northwestern Mediterranean. Here, a constant natural mortality (M) assumption is incorrect, as is the assumption that high fecundities are necessarily adequate for stock replacement. The high Ms-at-age for juveniles generated by the reciprocal model are shown to be a logical counterpart to the high fecundity of hake. Charnov’s criterion of intergenerational reproductive replacement is used to test for a sustainable population, analogous to a limit reference point warning of the dangers of overfishing beyond population replacement. Once peak mortality rates of age 2 hake exceed F(2)=1.1-1.2, which is currently the case, reproductive replacement may be at risk. Adult exploitation by inshore trawls is low, and maturing hake surviving the fine-mesh trawl fishery migrate offshore with a reduced vulnerability to fine-mesh gears. Early research suggested that rough bottom near the shelf edge once formed a refugium protecting offshore spawners from trawling, and led to abundant recruitment of juveniles nearer shore. It may not do so if offshore fishing effort by reinforced bottom trawls, gill nets and longlines is uncontrolled. Restoring offshore refugia to protect spawners and controlling peak fishing mortality of juveniles would be a precautionary strategy aimed at restoring previous levels of recruitment to the small-mesh trawl fishery.
Highlights
IntroductionThis study focuses on the mixed species small-scale trawl fishery of the northern Mediterranean capturing immature demersal fishes using the European hake Merluccius merluccius as an example, but has obvious relevance wherever juvenile fish are the focus of a fishery
Criteria for sustainable fisheries on juveniles illustrated for Mediterranean hake: control the juvenile harvest, and safeguard spawning refugia to rebuild population fecundity
This study focuses on the mixed species small-scale trawl fishery of the northern Mediterranean capturing immature demersal fishes using the European hake Merluccius merluccius as an example, but has obvious relevance wherever juvenile fish are the focus of a fishery
Summary
This study focuses on the mixed species small-scale trawl fishery of the northern Mediterranean capturing immature demersal fishes using the European hake Merluccius merluccius as an example, but has obvious relevance wherever juvenile fish are the focus of a fishery. Until the mid-1990s, the small-mesh trawl fishery operated sustainably without quotas or strict effort control (Ragonese 2009), and in a retrospective view of the fishery in the mid-1990s, Fiorentini et al (1997) noted a steady increase in landings of hake and many other species, suggesting that this reflected an increase in recruitment due to the increased productivity of formerly oligotrophic fishing grounds This environmental phenomenon may explain the anomaly that while landings were increasing, (Fiorentini et al 1997), assessments of European hake at earlier meetings of the General Fisheries Commission for the Mediterranean (GFCM) documented full to overfished status for Adriatic and Gulf of Lions stocks (see review by Caddy 2012, 2014a). Consistently low landings of European hake and other species were documented by Vasilakopoulos et al (2014), supposedly due to over-exploitation of juvenile fish
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