A joint stock assessment for the anchovy stock of the northern and central Adriatic Sea: comparison of two catch-at-age models

Abstract

Summary: Anchovy (Engraulis encrasicolus, L.) is one of the most important commercial species of the northern and central Adriatic Sea, as well as one of the most productive fisheries in the whole Mediterranean. In the Adriatic Sea the stock of anchovy is shared between Italy, Croatia and Slovenia. A joint stock assessment was carried out using catch data from all the fleets for the time interval . Analyses were performed using estimates of natural mortality at age obtained by means of two different methods and two population dynamics methods based on the analysis of catch-at-age data: LaurecSheperd virtual population analysis (VPA) and integrated catch-at-age (ICA), both tuned to acoustic estimates of abundance. Gislason's estimates for natural mortality appeared to be more realistic and were thus preferred for short-lived species. The general trend of biomass and fishing mortality is similar for the two models, highlighting the major collapse of the stock in 1987. Nevertheless, ICA has enough flexibility to combine all the data available without adding too much complexity in comparison with a VPA approach and seems to perform better in terms of the spawning stock biomass/recruitment relationship and diagnostics (i.e. the retrospective pattern). For the stock status, the exploitation rate from ICA is higher than the suggested threshold of 0.4 proposed by Patterson for small pelagic species.Keywords: Engraulis encrasicolus, Adriatic Sea, age-structured stock assessment, ICA, natural mortality, stock collapse.Evaluación conjunta de la población de la anchoa del Mar Adriático septentrional y central: comparación entre dos métodos de dinámica poblacional Resumen: La anchoa (Engraulis encrasicolus, L.) es una de las especies comerciales más importantes del mar Adriático central y septentrional, a la vez que es una de las actividades pesqueras más productivas en todo el Mediterráneo. La población de anchoa en el mar Adriático es compartida por Croacia, Italia y Eslovenia: una evaluación conjunta de la población fue realizada usando los datos de captura de todas las flotas para el periodo 1975-2009. Se efectuaron análisis usando estimaciones de la mortalidad natural por edad obtenidos mediante dos métodos diferentes y dos métodos de dinámica poblacional basados en el análisis de datos de captura por edad: Análisis de Población Virtual (VPA) de Laurec-Sheperd y Análisis de Captura Integrada por Edad (ICA), ambos acordados en las estimaciones acústicas de la abundancia. Las estimaciones de mortalidad natural de Gislason aparentaban ser más realísticas y por lo tanto daba preferencia a especies de vida corta. La tendencia general de la biomasa y de la mortalidad por pesca es similar en los dos modelos, destacando la fuerte disminución de la población en 1987. Sin embargo, ICA permite una flexibilidad suficiente para combinar todos los datos disponibles sin agregar excesivas complejidades con respecto al enfoque VPA y aparenta un mejor desempeño en términos de relación de SSB-R y en términos of diagnósticos (por ejemplo: ...

Analysis of Long-Term Changes in a Mediterranean Marine Ecosystem Based on Fishery Landings

“…For instance, anoxias in bottom waters linked to eutrophication occurred in the periods 1955-1956and 1972-1982(Sangiorgi and Donders, 2004, when the P/D index reached a value of ∼2. Finally, the P/D index showed an increasing trend in recent years (significant upward median-shift in 2009), probably linked to a partial recovery of small pelagic species, mainly European anchovy (Carpi et al, 2015).…”

Coupling Demographic and Genetic Variability from Archived Collections of European Anchovy (Engraulis encrasicolus)

“…Even though a significant reduction in H e in northern Adriatic anchovies is consistent with a bottleneck in N e and with a recent 10 to 20-fold drop in fishery biomass [ 19 , 20 , 22 ], the results from the heterozygosity excess test did not support this scenario. This outcome may be due to two mechanisms.…”

“…Genotypic data for CH78 and VI85 were used independently as founder populations to simulate bottleneck events lasting 32 and 25 generations, respectively. Population declines were tested using 1000 iterations with the following criteria: dioecious organisms with random mating system, balanced sex ratio (1:1), two years of expected lifespan for the species, given its high natural mortality [ 19 ], one year at first reproduction [ 24 ], and 90% generational overlap. The moment-based N e estimates from NE-ESTIMATOR were used as analogues of population size.…”

“…The Mediterranean area is one of the most exploited in the world with over 80% of its stocks are facing overexploited [ 18 ]. In recent years, European anchovy ( Engraulis encrasicolus , hereafter “anchovy”) stocks were over-exploited in two Spanish GSAs (Geographical Sub-Areas) (GSA 1 and GSA 6) [ 18 ], and signs of overfishing were found in the northern Adriatic Sea (GSA 17) [ 19 ]. Adriatic anchovy populations have experienced strong fluctuations over the past four decades [ 20 – 23 ].…”

The Saga of the Management of Fisheries in the Adriatic Sea: History, Flaws, Difficulties, and Successes toward the Application of the Common Fisheries Policy in the Mediterranean

“…Both species are fished all year round by pelagic trawlers and purse seiners covering great part of the basin, but mostly concentrated in the Northern part (Figure 2). Landings of anchovy have followed cyclic fluctuations over the years, with very high values in the late 1970s-early 1980s, partly attributed to the availability of subsidies from the European Community, and again in the late 2000s; both peaks were followed by a more or less marked decline (Carpi et al, 2015). The first, dramatic collapse was recorded in 1987 and has been attributed primarily to 2 years of very low recruitment, result of adverse environmental conditions: the fishery might have played a role in the disruption of the stock, nevertheless, the decrease in biomass started well before relevant changes in fishing effort were recorded (Santojanni et al, 2006).…”