Western Mediterranean Fisheries Research Articles

Spatial structuring of Mediterranean fisheries landings in relation to their seasonal and long-term fluctuations

The Western Mediterranean fisheries significantly contribute to the regional blue economy, despite evidence of ongoing, widespread overexploitation of stocks. Understanding the spatial distribution and population dynamics of species is crucial for comprehending fisheries dynamics combining local and regional scales, although the underlying processes are often neglected. In this study, we aimed to (i) evaluate the seasonal and long-term spatio-temporal fluctuations of crustacean, cephalopod, and fish populations in the Western Mediterranean, (ii) determine whether these fluctuations are driven by the spatial structure of the fisheries or synchronic species fluctuations, and (iii) compare groupings according to the individual species and life history-based groups. We used dynamic factor analysis to detect underlying patterns in a Landing Per Unit Effort (LPUE) time series (2009–2020) for 23 commercially important species and 33 ports in the Western Mediterranean. To verify the spatial structure of ports and species groupings we investigated the seasonal and long-term spatio-temporal fluctuations and common LPUE trends that exhibit non-homogeneous and species-specific trends, highlighting the importance of life history, environmental and demographic preferences. Long-term trends revealed spatial segregation with a north-south gradient, demonstrating complex population structures of Western Mediterranean resources. Seasonal patterns exhibited a varying spatial aggregation based on species-port combinations. These findings can inform the Common Fishery Policy on gaps challenging their regionalisation objectives in the Mediterranean Sea. We highlight the need for a nuanced and flexible approach and a better understanding of sub-regional processes for effective management and conservation – a current challenge for global fisheries. Our LPUE approach provides insight into population dynamics and changes in regional fisheries, relevant beyond the Mediterranean Sea.

Coviability analysis of Western Mediterranean fisheries under MSY scenarios for 2020

An ecosystem approach to fisheries (EAF) seeks to manage fisheries sustainably, including all dimensions of fisheries: biological, social and economic aspects. The separate management of these aspects may lead to conflicting objectives. Coviability analysis helps us to rank a set of choices (alternative management measures) objectively, allows us to explore which policies will ensure strong sustainability, and formally recognizes the multi-objective nature of fisheries management. The coviability of the main Western Mediterranean Spanish fisheries was examined with a bioeconomic simulation model under alternative management strategies that implement strong fishing mortality reduction policies. Based on a joint (biological and economic) viability assessment, it has been shown that Western Mediterranean fisheries require the reduction of fishing effort to ∼10% of the 2010 levels. This strong conservation measure would need to be applied as soon as possible in order for European Mediterranean fisheries to be managed at MSY, as required by legally binding international agreements, which may be unrealistic. Large reductions in fishing mortality for stocks that have been subject to high exploitation rates for decades are difficult to achieve with the current paradigm of effort control in the Mediterranean. Instead, reorienting the exploitation of Mediterranean fish stocks with management measures that combine changes in exploitation patterns with seasonal or spatial area closures, should help meet the policy goals of fishing mortality levels compatible with MSY by 2020.

Size at maturity, fecundity and reproductive potential of a protected population of the spiny lobster Palinurus elephas (Fabricius, 1787) from the western Mediterranean

Protected lobster populations are expected to contribute to the replenishment of fished populations through increased egg production. We studied the reproductive biology and egg production potential of a population of the spiny lobster Palinurus elephas protected from fishing since 1990 in the Columbretes Islands Marine Reserve (western Mediterranean). An index of spawning potential was derived to compare egg production potential in the Reserve and in western Mediterranean exploited populations. Females' physiological maturity (ability to reproduce) and functional maturity (ability to mate and bear eggs) occurred at a carapace length (CL) of 76–77 mm. Males' physiological maturity occurred at a slightly larger size, 82.5 mm CL. In the Reserve, P. elephas' individual fecundity increases linearly with body size up to the females' maximum size, although maximum reproductive yield (eggs per body gram) was reached at intermediate sizes. Size-specific fecundity in the protected population was similar to that of lightly fished populations off Ireland and greater than that of western Mediterranean exploited populations. The female size class of 105–110 mm CL contributed most to egg production in the protected population and is well above the minimum landing size (MLS) for western Mediterranean fisheries. Newly mature females (below MLS) generate a very small fraction (1%) of the egg production from the Reserve. Given the pattern of exploitation in western Mediterranean fisheries, egg production potential depends more on the quantity than on the mean size and fecundity of the available females. The role of the greater availability of large males for mating in unfished populations is discussed in terms of the females' individual fecundity and mating success.

Long-term changes in the trophic level of western Mediterranean fishery and aquaculture landings

We explored changes in western Mediterranean fishery and aquaculture landings using trophic level (TL) estimates derived from nitrogen stable isotope analysis combined with geographically detailed fishery data collated by the General Fisheries Council for the Mediterranean (GFCM). Our analyses confirmed earlier suggestions that there has been a significant decline in the mean trophic level of Mediterranean landings (by ~0.15 TL over 26 years). However, this decline is suggested to be almost entirely a result of increased landings of bivalve molluscs from mariculture and not due to changes in landings from capture fisheries. The mean trophic level of finfish landings has not changed significantly since 1973, although both fish and total landings have become significantly more diverse. Inspection of small pelagic fish landings revealed a marked decrease in the contribution played by anchovy and replacement of this species by sardine. Since 1981, cage culture of high trophic level species such as sea bass (Dicentrarchus labrax) and seabream (Sparus aurata) has become increasingly important, such that when clupeoid landings were excluded from the analyses, the mean trophic level of finfish landings was actually demonstrated to have increased over the past 26 years.

Feeding ecology of the loggerhead turtle Caretta caretta in the western Mediterranean

AbstractWe studied the feeding ecology of juvenile loggerhead turtles Caretta caretta in the western Mediterranean based on the contents of the digestive tract of 54 turtles (range of CCL: 34–69 cm) seized in Barcelona (Spain) in 1991. Turtles had been captured in fishing trawls, but specific information about dates and localities is not available. Despite this limitation, we obtained interesting evidences about the foraging strategies of loggerheads, with potentially important conservation implications. We report 33 new taxa in the diet. Results indicated that western Mediterranean loggerheads feed in an opportunistic way. Numerically, fish made up the most important prey group, followed by pelagic tunicates, crustaceans, molluscs and other invertebrates. The importance of fish as a food resource has been rarely reported, and several lines of evidence indicated that fish were possibly consumed as discarded by‐catch. This raises the question over whether or not western Mediterranean fisheries are an important food source for juvenile loggerheads. The number and diversity of prey increased with turtle size, this may reflect the lack of prey selectivity of juvenile loggerheads coupled with a higher retention of food remains in larger turtles. Discounting prey that could be consumed as discarded by‐catch, dietary data suggest that most, if not all, loggerheads of our sample were captured in neritic habitats. However, many turtles contained remains of both pelagic and benthic‐demersal prey. These observations support the existence of an intermediate neritic phase in loggerheads' developmental shift from pelagic–oceanic to benthic–neritic foraging habitats, as previously suggested. During this phase, loggerheads would feed upon both pelagic and benthic prey.

Application of generalized linear modeling to catch rate analysis of Western Mediterranean fisheries: the Castellón trawl fleet as a case study

Generalized linear modeling (GLM) is used to analyze hake catch rates in the Spanish trawl fleet fishing off Castellón (E Iberian Peninsula) between 1991 and 1996 and to provide consistent indices of abundance. Main effects in the models include a factor for vessel tonnage, to adjust for characteristics that determine fishing power, as well as factors for year, month and fishing closure. Vessel tonnage, season and year are shown to have a significant effect on hake catch rates, with vessel capacity alone explaining about 54% of the total variation in the data. Significant interactions indicate that monthly fluctuations in catch rates differed by year probably in relation to the timing of hake recruitment and of the bimonthly annual closure of the fishery. Hake abundance indices, as derived from the year coefficients in the model, were intermediate in 1991 and 1992, low in 1994 and 1995 and high in 1993 and 1996. This result is corroborated by abundance indices from survey estimates for the later years. The model explains 63% of the variation in the CPUE data, which is similar or above of what has been found by other authors in comparable studies for fisheries around the world. Thus, the modeling approach of catch rates from trawl fisheries offers a promising method for obtaining standardized abundance indices of groundfish stocks in the Western Mediterranean. Further application is the study of area effects on catch rates of fleets sharing the same resource in the region.