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The sex ratio, length–weight relationship (LWR) and diets based on stomach contents of whiting (Merlangius merlangus) were investigated in the south-eastern Black Sea, Turkey. A total of 3507 females (7.5–24.0 cm), 1602 males (9.4–20.0 cm), and 78 unidentified sex (5.5–16.5 cm) whiting were caught during monthly sampling from February to December 2017. The sex ratio was dominated by females, and their ratio (♀:♂, 1:0.46) significantly deviated from 1:1. The LWR indicated a negative allometric growth for males, while females had a positive allometric growth pattern. The stomach content analysis based on the relative importance index (IRI%) indicated exclusively piscivorous diets dominant by Sprattus sprattus and Engraulis encrasicolus made up more than 91 IRI% of the total diets of M. merlangus. The modified Costello-Amundsen's graphical analyses evinced the specialized feeding strategy of M. merlangus throughout this study. The contribution of these two preys to the diets of M. merlangus showed considerable seasonal variations that were totally dependent on their abundance. Sprattus sprattus contributed to more than 98% of the total diets during June, July and August, while in the following months, E. encrasicolus appeared to take its position. Based on fish size, a general trend of a rise in prey diversity was found with increasing fish size. Also, the contribution of S. sprattus tended to decrease with increasing predator size, which is replaced by a rise in E. encrasicolus contribution. Hence, larger M. merlangus predominantly fed on E. encrasicolus while smaller size predators preferred to feed on S. sprattus. [ABSTRACT FROM AUTHOR]

Status assessment of exploited fish populations is a general requirement to ensure sustainability of fisheries in both global and local contexts. The blue jack mackerel Trachurus picturatus (Bowdich, 1825) remains unassessed in a data-limited fishery in the eastern central Atlantic, within the waters of the Canary Islands (Spain) off the coast of northwest Africa. This is the most southwestern targeted fishery in the species' distributional range. To obtain basic life-history information, a total of 2 472 specimens were analysed, ranging from 10.2 to 31.9 cm total length, from samples collected monthly between March 2005 and March 2006. Length-weight relationships (a = 0.0023; b = 3.418; R2 = 0.97) showed no significant difference between sexes. Deposition periodicity and coherence of the ageing criteria were verified by analysis of the monthly evolution of the otolith edge. Ages were estimated by counting annual growth rings on whole otoliths, with these fish ranging from age 0 to 6 years. The von Bertalanffy growth model, which was used to estimate growth parameters from both direct readings and back-calculated length-at-age data, gave good statistical fits. The parameters from the direct readings were: L∞ = 34.9 cm; k = 0.214 y-1; t0 = −2.545 y (R2 = 0.84), and the natural mortality rates estimated from empirical methods varied between 0.20 and 0.55 y-1. [ABSTRACT FROM AUTHOR]

Increased global demand for bluefin tuna has triggered unsustainable fishing and many wild stocks have seen dramatic declines. Improved fisheries governance is now slowly stabilizing many stocks and recently bluefin aquaculture has emerged as an economic alternative route for supplying the market. Most of captured bluefin tuna directly enters the global seafood market, but an increasing part of catches are destined to aquaculture (17-37%) as bluefin aquaculture almost exclusively depends on wild specimens for stocking. Farming is mainly being performed in the Mediterranean region, Mexico, Australia, and Japan. Few studies have focused on the global importance and future role of bluefin aquaculture and there are confounding uncertainties related to production volumes and trends. This study provides an overview of global bluefin tuna aquaculture and identifies its direct and indirect interactions with wild fish stocks, outlines some of the challenges for future expansion as well as pointing out significant mismatch of production statistics. [ABSTRACT FROM AUTHOR]

Millions of tons of increasingly scarce small pelagic fish that could be directly consumed as inexpensive high-quality protein have been diverted to rendering plants for fish oil and fishmeal to sustain the aquaculture of expensive fish in more prosperous countries. Critics argue that this imperils the food security of the poor people in developing countries off whose coasts the fish are often caught. However, others assert that the actual demand for these small fish for the dinner table is slight and that plant or by-product-based pellets are increasingly substituting for all or part of the fish feed. The latter trend may allow for closely monitored catches of small pelagics during the transition to sustain continuing growth and high levels of employment in aquaculture. [ABSTRACT FROM PUBLISHER]

The development of suitable reference states for ecosystem-based management requires documentation of changes in structure and functioning of marine ecosystems, including assessment of the relative importance of bottom-up and top-down processes as drivers of change. We used monitoring data available from St Helena Bay, the most productive bay and an important nursery area situated on the west coast of South Africa, during 1950–2010 to reveal changes in the abiotic and biotic components. St Helena Bay in the 1950s showed similarities to 2000–2010 in terms of wind patterns, hydrology and phytoplankton. Upwelling, oxygen and nutrient concentrations in subthermocline water displayed pronounced decadal-scale variability. Primary production in St Helena Bay is variable, but consistently higher than that on the adjacent Namaqua shelf. Zooplankton size composition and biomass in August have changed markedly since the 1950s. During 2001–2010, mesozooplankton biomass in autumn was considerably lower than in summer, probably due to predation by small pelagic fish. Pelagic fish catch patterns and distributions have altered dramatically. Conservation measures, implemented to reverse past negative human impact, have benefitted marine mammals, the abundance of which has increased in the area, but additional conservation measures are necessary to reverse the decline in African penguins Spheniscus demersus. St Helena Bay shows a muted response to long-term change in the southern Benguela, with marked decadal variability but no clear long-term trend in oceanography and biogeochemistry. Changes in ecosystem boundary conditions and fishing pressure cannot be ignored as important drivers of change in the southern Benguela since the 1950s. [ABSTRACT FROM AUTHOR]

Once one of the most numerous seabirds of the Benguela upwelling system, the population of Cape cormorants Phalacrocorax capensis has decreased by 60% in the past three decades and the species is listed as Near Threatened. Declines in prey availability and/or abundance brought about by recent changes in the distribution of pelagic fish stocks and industrial purse-seine fishing are hypothesised to be a key driver of seabird population decreases in the southern Benguela. We investigated the foraging behaviour of breeding Cape cormorants by deploying GPS and temperature–depth recorders on 24 breeding adults from three islands off the coast of South Africa, two of them to the north of Cape Point and a third farther south on the western Agulhas Bank. This provided the first measures of foraging dispersal by a cormorant in the Benguela system, and enabled a comparison of foraging behaviour between birds from these islands. Foraging trips of Cape cormorants lasted between 17 min and >7 h, at a maximum distance of between 2 and 58 km away from their colony. Foraging effort was significantly greater for birds from farther north off the West Coast in terms of trip duration, distance travelled, number of dives and time spent flying compared to those from the southernmost island (Dyer), which is probably a response to low prey availability in the north. Coastal reserves that exclude pelagic fishing from inshore feeding grounds around Cape cormorant breeding colonies may result in increased local prey availability, which would benefit Cape cormorant populations. [ABSTRACT FROM AUTHOR]

The main results of research work carried out since 1998 with regard to the application of hydro-acoustic technologies for the evaluation of biomass and distribution of small pelagic fish species off the southern coast of Sicily are presented, taking into account information from hydrology and from ecology of the fish populations targeted. The biomass estimates and the population-density charts presented concern the two main species, i.e. sardine Sardina pilchardus (Walbaum, 1792) and anchovy Engraulis encrasicolus (Linnaeus, 1758). Both the sardine and anchovy populations experienced large inter-annual fluctuations, with biomass estimates ranging from 6000 to over 36,000 tonnes (t) (sardine) and from about 7000 to 23,000 t (anchovy). Acoustic estimates are largely consistent with landings recorded in Sciacca (the main fishing port for small pelagic species in the study area) during the year following the evaluation surveys. In addition, trends in sardine and anchovy biomass estimates appears to be negatively correlated with the mean sea surface temperature calculated over the time intervals January-September (sardine) and June-November (anchovy) of the preceding year, which correspond to larval and juvenile growth periods of target species. Observed patterns would suggest the importance of enrichment processes relevant to the survival of early stages, so determining recruitment success and finally higher population sizes. [ABSTRACT FROM AUTHOR]