Scientia Marina

Foreword

Rosario Domínguez-Petit — 2022-12-14

A reconceptualization of the interactions between spawning and growth in bony fish

Daniel Pauly — 2022-12-14

Among fishery biologists and even ichthyologists, maturation and spawning of fish are viewed as processes that use “energy” that would otherwise be applied to somatic growth, which is supposed to explain why post-maturity growth in length tends to decline. This widespread conceptualization may be called the “reproductive drain hypothesis” (RDH). However, when growth is correctly viewed as involving body mass, and is thus expressed in weight, post-maturity turns out (in iteroparous bony fish whose maximum length exceeds 10 cm) to accelerate after first maturity, despite its energy cost. This, and other common observations flatly contradict the RDH, and the time has come to withdraw this hypothesis. As a contribution towards this task, we propose an alternative reconceptualization of fish spawning consistent with what is known about fish biology.

Expansion and contraction of the Engraulis ringens spawning area in northern Chile

Paola Moreno — 2022-12-14

Many studies have considered the temporal patterns of reproduction of Engraulis ringens, but little attention has been given to the spatial patterns of reproduction (spawning areas), which have shown great variability in both location (geographical position) and extent (the area covered by positive stations), without a satisfactory explanation. Along the Chilean coast, the daily egg production method (DEPM) has been used for several years to estimate spawning biomass in the northern Chile E. ringens population, with 24 surveys being carried out from 1992 to 2020. The most fluctuating parameters estimated in the DEPM have been the location and extent of the spawning area and the average female weight. In the last few years the eggs were distributed near the coast, whereas in the first few years they showed a more oceanic distribution. The average female weight has fallen from 30 g in the 1990s to 11 g in the last few years. In the present study, we analysed the relationship of the location and extent of spawning areas with female size and abundancy in E. ringens from northern Chile. According to the results, periods of high abundancy of eggs are positively correlated with larger females that spawn in more oceanic zones and to the south, expanding the spatial egg distribution and increasing the egg density. By contrast, in years with low abundance of eggs, the spawning was located north and towards the coast, with a smaller spawning area and smaller female size.

Assessing changes in size at maturity for the European hake (Merluccius merluccius) in Atlantic Iberian waters

Davinia Lojo — 2022-12-14

European hake (Merluccius merluccius) is a commercially important resource in Iberian Atlantic waters. Despite the recovery plan implemented in 2006 and the multiannual management plan for western waters, fishing mortality is still higher than that corresponding to the maximum sustainable yield for the southern European hake stock. The biological processes underlying the dynamics of this stock and its life history traits are essential for assessing population productivity and resilience, making them basic information for management. We analysed the temporal variability of size at maturity (L₅₀) of this species and the main factors influencing it in Atlantic Iberian waters from 1982 to 2019. The annual variability of L₅₀for each sex was modelled with generalized additive models, considering explanatory environmental variables (Atlantic Multidecadal Oscillation, North Atlantic Oscillation and sea surface temperature) and biological variables (biomass, spawning biomass at length and relative condition factor). The results showed that the L₅₀ of males decreased by a total of 12.9 cm and L₅₀ of females decreased by a total of 10.9 cm from 1982 to 2019. For females the significant explanatory variables were year, spawning biomass at length, biomass and the North Atlantic Oscillation, while for males only year was an explanatory variable. These results are important for understanding the status of the European hake population, signalling that L₅₀is a good indicator for predicting future population dynamics.

Reproduction of grey snapper (Teleostei: Lutjanidae) in the southern Gulf of Mexico

Karina del C. Macal-López — 2022-12-14

Snappers exhibit reproductive trait plasticity in response to habitat distribution. Lutjanus griseus is among the most economically important snappers in the western Central Atlantic but has received limited study in the region. Data on the reproductive biology of the L. griseus population were collected on the continental shelf of the Yucatan Peninsula, Mexico. Over a nineteen-month period, 1236 specimens were captured monthly in three Yucatan artisanal fishing fleet operational areas. Data were grouped by month to generate an annual analysis. Individual sex and maturation status were identified by gonad histology. Median size did not differ between females (33.2 cm fork length [FL]) and males (33.3 cm FL), and the sex ratio was balanced (F:M=0.98:1.00). Size at maturity was 24.2 cm FL for females (38% of maximum size reported for the species) and 22.8 cm FL for males (36% of maximum size), and the spawning season ran from May to September. The results confirm that this population exhibits the typical reproductive pattern of snappers distributed on continental shelves or in shallow water areas and provide critical data for stock assessment and implementation of management measures for L. griseus stock in the southern Gulf of Mexico.

Spatial variability of life-history parameters of the Atlantic chub mackerel (Scomber colias), an expanding species in the northeast Atlantic

Rosario Domínguez-Petit — 2022-12-14

Atlantic chub mackerel is a pelagic species present in the Atlantic Ocean that in recent decades has expanded northwards in the eastern Atlantic. Fish samples were collected in scientific surveys and commercial catches between 2011 and 2019. We analysed the geographical variation of the biological parameters (age, length, weight and condition), as well as the length-weight relationship, maturity-at-length and spawning season onset and duration in five geographical areas (from south to north): the Canary Islands, Gulf of Cadiz, western Portuguese coast, northwestern Spanish coast and Cantabrian Sea. The influence of sea surface temperature (SST) on fish length was modelled as a potential driver of geographical variability. All biological parameters increased progressively northwards, while the spawning season was delayed and prolonged with increasing latitude, from January in the Canary Islands to May-August in the Cantabrian Sea, when SST was between 15°C and 19°C. SST had a positive effect on length in three study areas and a negative one in two of them, suggesting that each group is at a different position within their thermal tolerance range. Deviance from the geographical pattern of some biological parameters in the Gulf of Cadiz suggests that it could be a hinge or mixing zone between Atlantic African, Mediterranean and Atlantic Iberian population components.

RNA/DNA and derived condition indices for anchovy and hake larvae as relevant information for comprehensive fisheries management

Marina V. Diaz — 2022-12-14

The nutritional condition of anchovy and Argentine hake larvae in the Northern Patagonian Frontal System (NPFS) area was studied in the austral spring of 2018. We hypothesized that this area provides adequate features for larval growth and survival. The RNA/DNA index (RD) and its derived index of growth performance were employed. A critical RD value for starvation was calculated. The percentage of individuals under starvation and in optimal growth conditions was calculated. Because the period of study was the beginning of the hake spawning period, a limited number of larvae of this species were collected. The RD index showed a significant increase throughout larval ontogeny for anchovy larvae, being 1.84±1.39 (N=739) and 2.77±1.50 (N=220) in the pre-flexion and flexion stages respectively. These values were significantly higher at stations close to the NPFS and at the upper level of the water column. No differences were observed throughout the day. The area inside the NPFS showed a lower proportion of starved anchovy and a higher proportion of individuals in optimal growth, standing as a favourable nursing area. For hake larvae, the average RD was 1.64±0.55 (N=15). The great sensitivity of the RD index makes it a powerful tool for assessing the probability of larval survival and posterior recruitment into fisheries and allowing the identification of favourable rearing areas for these important species for fisheries.

Influence of maternal effects and temperature on fecundity of Sebastes fasciatus on the Flemish Cap

Francisco González-Carrión — 2022-12-14

The conservation of a sufficient reproductive potential of an exploited stock is one of the goals of fisheries management, as it ensures sustainable productivity. However, there is evidence that spawning stock biomass (SSB) does not represent well the variation in stock reproductive potential, often leading to impaired stock-recruitment relationships. In this study we show that fecundity of Sebastes fasciatus on Flemish Cap is not proportional to SSB and shows temporal fluctuation influenced by maternal effects. Females were collected in 23 research surveys between 1996 and 2020. An autodiametric calibration model was developed for S. fasciatus for the first time to estimate fecundity. Mean potential fecundity was estimated as 36000 oocytes and mean relative fecundity as 79 oocytes g^–1. Potential fecundity varied significantly with female length, age, condition index, gonadosomatic index and environmental variability. Mixed-effect linear models were fitted to assess the effect of maternal traits and bottom temperature on fecundity. Fecundity increased significantly with condition factor and sea bottom temperature. Relative fecundity also increased significantly with length, age and gonadosomatic index, indicating that older, larger and better-conditioned females produce more eggs per female gram. This suggests that SSB is not a good proxy to stock reproductive potential so it is unsuitable for use in stock assessment and scientific advice. Considering that S. fasciatus is a viviparous species, future research should focus on maternal effects on offspring and on building time series of reproductive potential indexes that take into account maternal effects.

Spawning area of the tropical Skipjack Tuna, Katsuwonus pelamis (Scombridae), in the western Mediterranean Sea

Miguel Angel Puerto — 2022-12-14

Skipjack is an important commercial species with a tropical distribution, although captures in the Mediterranean Sea have been recorded for decades. The western Mediterranean Sea, specifically the Balearic Sea, is a spawning area for several tuna species. We hypothesized that the western Mediterranean warming in the last few decades could lead to the expansion of skipjack tuna spawning areas from tropical areas to the Mediterranean Sea. We analysed 454 individuals (41.8-81 cm straight fork length) caught by sport fishing vessels in offshore trolling championships in Spanish Mediterranean waters during summer months from 2014 to 2019. Analysis of the gonadosomatic index and microscopic examination of the ovaries (n=192) showed that the skipjack is reproductively active in the western Mediterranean, particularly in the Balearic Sea. These results indicate that the skipjack has expanded its distribution and spawning area from tropical waters to the Mediterranean, probably owing to the gradual warming detected in the area in the last few decades. This new spawning activity in the area should be monitored in the near future to study the possible impact on other tuna species that share the distribution range and spawning area with skipjack tuna in the western Mediterranean.