Criteria for sustainable fisheries on juveniles illustrated for Mediterranean hake: control the juvenile harvest, and safeguard spawning refugia to rebuild population fecundity

Abstract

Summary: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.Keywords: harvesting juveniles; European hake; natural mortality at age; population fecundity; spawning refugia; intergenerational ratio; Charnov's criterion; Mediterranean Sea.Criterio para una pesca sostenible de juveniles, tomando como ejemplo la merluza del Mediterráneo: control de la pesca de juveniles y preservación de refugios para reproductores, con el fin de rehacer la fecundidad de la población Resumen: Este artículo presenta varios temas de relevancia para la gestión pesquera de juveniles que contrastan con las evaluaciones de estocs pesqueros basados en la aproximación de Beverton y Holt (1957) para una explotación racional de los peces maduros. En concreto, se presenta un ejemplo para la pesquería de juveniles de merluza europea, Merluccius merluccius, en el Mediterráneo noroccidental. En este caso, es incorrecto asumir la mortalidad natural (M) como constante, como lo es asumir que se necesitan fecundidades elevadas para la adecuada reposición de los estocs. Se demuestra cómo los elevados valores de M por edad para los juveniles generados con el modelo recíproco son la contrapartida lógica a la elevada fecundidad que presenta la merluza. El criterio de Charnov sobre el reemplazo intergeneracional del estoc reproductor se utiliza como test para una población sostenible, análogo a un punto límite de referencia que avisa sobr...

First Large-Scale Eastern Mediterranean and Black Sea Stock Assessment Reveals a Dramatic Decline

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Essential fish habitats and hotspots of nekto‐benthic diversity and density in the western Mediterranean

“…Some researchers have suggested limiting juvenile exploitation through implementing management plans and strengthening compliance, control, and enforcement (Vasilakopoulos et al, ); or, additionally, improving gear selectivity by increasing mesh size (Colloca et al, ). Conversely, others have recommended restoring the ‘Mediterranean paradigm’, which advocates reducing the fishing effort on offshore spawning grounds (‘spawners refugia’), whilst limiting inshore trawling effort on juveniles (Caddy, ). Total allowable catches have also been proposed in order to achieve fishery policy objectives before 2020 (Cardinale & Scarcella, ).…”

Size-dependent survival of European hake juveniles in the Mediterranean Sea

“…The modelling of juvenile harvest and how to estimate and implement realistic vectors of natural mortality in the assessment and management of this species have been important topics of research in the last two decades (e.g. Abella et al 1997, Caddy and Abella 1999, Caddy 2015. To this end, scientificallybased information is required to disentangle ecological processes that affect their survival (i.e.…”

“…are less available to bottom trawl gears (thanks to spawning refugia; Colloca et al 2013, Caddy 2015 and references therein), although they are targeted by other commercial gears such as longlines and gillnets in some Mediterranean areas (Aldebert et al 1993, Sbrana et al 2007. All of these findings evidence the high importance of having a complete view of the juvenile life stage to understand how the combination of ecological, environmental and fishing impact shapes natural mortality (Jørgensen et al 2013), a key population dynamics parameter normally assumed to be constant and age-independent in the assessment frameworks (Abella et al 1997, Caddy 2015.…”