The Seasonal Distribution of a Highly Commercial Fish Is Related to Ontogenetic Changes in Its Feeding Strategy

Abstract

Improving the knowledge on the biology, ecology and distribution of marine resources exploited by fisheries is necessary to achieve population recovery and sustainable fisheries management. European hake (Merluccius merluccius) is one of the most important target species in the Mediterranean Sea and is largely overexploited by industrial fisheries. Here, we used two methodological approaches to further investigate the seasonal variation in the spatial distribution of European hake considering ontogenetic changes and trophic ecology in the western Mediterranean Sea. Our main aim was to explore if spatial changes in hake distribution were related to trophic behavior, in addition to key environmental factors. We employed a hierarchical Bayesian species distribution modeling approach (B-SDM), using spatial data from two oceanographic surveys conducted during winter and summer. We analyzed how the environmental variables, together with abundance and mean weight distribution of the main preys identified for European hake, affected the seasonal distribution of the species. Results revealed clear differences in the distribution of the European hake between seasons, which were indeed partially correlated to the distribution of their main preys, in addition to the environment. Stable isotope values and Bayesian isotopic mixing models (MixSIAR) revealed substantial seasonal and ontogenetic differences in trophic habits of European hake, partly matching the spatial distribution results. These findings could have implications for a future seasonal-based adaptive fisheries management, as local depletion of prey, or variation in size and condition may affect European hake presence in this area. Moreover, this study illustrates how the sequential application of methodologies provides a more holistic understanding of species seasonality, which is essential to understand the phenological processes of exploited species and their potential shifts due to environmental changes.

Optimum growth temperature declines with body size within fish species

“…Whether the largest fish of a population will be the first to experience negative effects of warming, as suggested by the finding that optimum growth temperature declines with body size, depends on the environmental temperatures they typically experience compared to smaller conspecifics. For instance, large fish may inhabit colder temperatures compared to small fish due to ontogenetic habitat shifts (Lloret-Lloret et al, 2020; Werner & Hall, 1988); see also Heincke’s law (Audzijonyte & Pecl, 2018; Heincke, 1913). Yet, there is already empirical evidence of the largest individuals in natural populations being the first to suffer from negative impacts of warming, either from increased mortality (Peralta-Maraver & Rezende, 2021; Pörtner & Knust, 2007), or not being able to increase growth rates as smaller conspecifics tend to do (Huss et al, 2019; van Dorst et al, 2019).…”

Using molecular and stable isotope markers to identify the main predators of Nephrops norvegicus in Mediterranean deep-water ecosystems

“…The range of values found suggests that some predators can exploit resources across entire food webs. L. budegassa and A. veranyi both showed the highest values, indicating that they may prey on other potential predators, such as Merluccius merluccius, and even other cephalopods (Negzaoui-Garali et al 2008, López et al 2016, Guerra-Marrero et al 2020, Lloret-Lloret et al 2020. The overlap in the different isotopic niches helped us determine if the diet composition of each predator was similar to that of a predator that only consumes N. norvegicus.…”

Multiscale analysis on otolith structural features reveals differences in ontogenesis and sex in Merluccius merluccius in the western Adriatic Sea

“…The European hake ( Merluccius merluccius ) is a major component of the demersal fish assemblages and is distributed over a wide depth range (20–1000 m) throughout the Mediterranean Sea and the northeast Atlantic region [ 12 ]. The hake is an important predator of deeper-shelf, upper-slope Mediterranean communities.…”

“…Subsequently, juvenile hakes migrate from the nursery areas to the parental stock, and when they reach a total length between 18 and 32 cm, they gradually change their diet towards pelagic and necto-benthic fish such as Sardina pilchardus and Engraulis encrasicolus [ 15 , 16 ]. These preys inhabit the coastal continental shelf and form schools usually deeper than 25 m [ 12 ]. Moreover, such trophic shifts coincide with an increase in the area of the inner ear of hake responsible for the detection and localization of objects, which takes place approximately at the critical size of 14–15 cm and could be important in detecting mobile prey such as fish [ 19 ].…”