Atlantic Chub Mackerel Scomber Colias Research Articles

Estimates of the Fecundity of the Atlantic chub Mackerel Scomber colias (Gmelin, 1789) in the Northeast Atlantic and Mediterranean Moroccan Coasts

Estimates of the Fecundity of the Atlantic chub Mackerel Scomber colias (Gmelin, 1789) in the Northeast Atlantic and Mediterranean Moroccan Coasts

Post-mortem ‘soft flesh’ in three commercial fish species from off Atlantic Morocco associated with the myxosporean parasites Kudoa thyrsites and K. encrasicoli (Myxozoa)

Small pelagic fishes represent one of the most important food resources off the Northwest coast of Africa. Despite their economic significance, little is known about the infections with flesh invading myxosporean parasites of genus Kudoa (Cnidaria, Myxozoa). Heavy infections in the flesh may be associated with post-mortem myoliquefaction, commonly known as ‘soft flesh’. This condition may reduce the quality and marketability of the fish fillet, resulting in both economic losses to the fishing industry and loss of consumer confidence. In this study, we investigated Kudoa-induced ‘soft flesh’ occurrence in European anchovy Engraulis encrasicolus, European pilchard Sardina pilchardus, and Atlantic chub mackerel Scomber colias caught in 2019 off the Moroccan Atlantic coast. Five hundred specimens of each fish species were examined for ‘soft flesh’ by texture testing and visual inspection 48 h post-catch. ‘Soft flesh’ occurred in 0.2 % of the European anchovies, 1.4 % of the European pilchard, and in 4.4 % of the Atlantic chub mackerel. Microscopic examination of muscle samples revealed that ‘soft flesh’-affected fish were infected with myxospores of K. thyrsites-like morphotype. Analysis of the kudoid SSU rDNA sequence obtained from European pilchard and the Atlantic chub mackerel identified these as K. thyrsites (100 % identity), whereas analysis of the sequence from European anchovy identified the presence of K. encrasicoli (100 % identity). Even if there are no known human health consequences associated with the ingestion of these Kudoa species, the unsightly appearance of some infected fillets is a food quality issue, that can eventually lead to reduced marketability and value.

Age affects otolith shape in a coastal pelagic fish (Scomber colias Gmelin, 1789)

Otolith shape analysis is a common and efficient technique to study the population structure of fish species. This approach compares the overall otolith shape among individuals collected along the species´ distribution range. Otolith shape may change during ontogeny; thus, comparing otolith sample collections comprising multiple and variable age classes may lead to biased results. Therefore, it is crucial to test for possible effects of age on the otolith shape for a given species before interpreting potential differences in otolith collections. Here, we explored the effect of age on the otolith shape of a coastal pelagic fish species with a wide geographical distribution and fast growth rate, the Atlantic chub mackerel Scomber colias (Gmelin, 1789). This effect was tested across different years using different age assignment techniques (direct age reading and age back-calculation) and otolith shape descriptors (Elliptic Fourier and Discrete Wavelet). The results show that the age effect on otolith shape is most noticeable between age-1 and older fish, possibly due to rapid growth during the first year of life. Also, the age effect on otolith shape depended on the descriptor used, being more detected when using the Discrete Wavelet descriptor compared to Elliptic Fourier. Our results highlight the need to carefully examine age effects on otolith shape before conducting population structure analysis on mixed-age sample collections.

Maturity length, fecundity and spawning season of Atlantic chub mackerel Scomber colias in the coastal waters of Ghana (west-central Gulf of Guinea)

Aspects of the reproductive biology of Atlantic chub mackerel Scomber colias are reported here based on data from random samples of artisanal fish landings from Ghana. The specimens were between 13.7 cm and 40.7 cm total length (TL), and both sexes matured at a mean length (L m50) of approximately 25 cm TL. An overall sex ratio of 1:1 was estimated for the population. Absolute fecundity of the fish ranged between 10 220 and 155 791 eggs (mean 48 238 [SE 2 324] eggs) in individuals measuring between 22.8 and 36.5 cm TL and weighing 104.3 to 525.3 g. Monthly variations in the gonadosomatic index and the proportion of fish with ripe gonads in the samples indicated the occurrence of spawning activities during two periods, March–April and June–August, the latter period of which coincided with the coastal upwelling season in Ghanaian waters. These findings are compared with those for chub mackerel from the northwestern and southwestern coasts of Africa. The results of this study will help inform the management of this small pelagic species in Ghana.

Population Dynamics of Atlantic Chub Mackerel Scomber colias at the Multispecies Fishery

Population Dynamics of Atlantic Chub Mackerel Scomber colias at the Multispecies Fishery

Diet and trophic position of two mackerel species in the archipelago of Madeira, Portugal

The Atlantic chub mackerel Scomber colias and the blue jack mackerel Trachurus picturatus are two abundant species in the Macaronesia region which includes the archipelago of Madeira, Portugal. Both are key species in the trophic web, being important prey for several local top predators, such as seabirds and marine mammals. Nonetheless, little is known about their feeding ecology in oceanic environments. In this study, the authors describe the seasonal variation in the diet of S. colias and T. picturatus in the oceanic region of Madeira throughout a year. Visual inspection of stomach contents revealed that S. colias fed on a broader range of prey groups than T. picturatus, but for both species, zooplankton (particularly calanoid copepods) and fish were the most important food items. The diet of S. colias included a higher proportion of fish, namely Atlantic saury Scomberesox saurus and S. colias, than that of T. picturatus, that included mostly the longspine snipefish Macroramphosus scolopax. T. picturatus consumed a higher proportion of decapods and other copepods. Seasonal variation was found in the diet of both species, with zooplanktonic species being more important in colder months (February to April) for S. colias and during warm months (May to October) for T. picturatus. Their diet in other seasons was dominated by fish. Although they consume similar prey, carbon and nitrogen stable isotope analysis of muscle of S. colias and T. picturatus showed little overlap in their diets, and T. picturatus showed higher δ15 N and a narrower isotopic niche.

Tunas off northwest Africa: The epipelagic diet of The Bigeye and Skipjack tunas

Tunas are among the most exploited top predators worldwide, with negative impacts on some of their stocks. Changes in their population abundance can impact marine food-webs and have the potential to alter entire ecosystems. To better understand the impacts of the exploitation of tuna stocks in the most critical habitats, basic knowledge on the diet of these species in each region is required. Here, we describe the diet of the two most fished tuna species in the archipelago of Madeira, the Bigeye tuna Thunnus obesus and the Skipjack tuna Katsuwonus pelamis, based on stomach contents analysis. To gain further insights into the diet, and also better assess the possible bias caused by the occurrence of live bait in stomachs, we compared tuna mercury values with those of two other predators with similar diets that are not directly targeted by fisheries, and with Bigeye and Skipjack tunas from other ocean basins. Bigeye tunas fed mostly on Atlantic chub mackerel Scomber colias and mackerel Trachurus sp., which together contributed with 85% of total prey weight. Only 7.5% of prey weight was constituted by mesopelagic prey, including myctophids and cephalopods. Skipjack tunas had an epipelagic diet (NF = 97%), with the Atlantic chub mackerel representing half of the total prey weight, despite Longspine snipefish Macroramphosus scolopax and Sand smelt Atherina sp. accounting for 62.9% of the total number of prey. There were interannual variations in diet likely linked to interannual pelagic community shifts. Bait did not bias the results of the stomach analysis of these tunas and bait species were observed to be part of the natural diet of both tuna species. Baseline data provided by this study should allow for more informed decisions for an efficient ecosystem-based fisheries management.

Seabird diet analysis suggests sudden shift in the pelagic communities of the subtropical Northeast Atlantic

The dynamics of the subtropical pelagic ecosystems of the Northeast Atlantic are still poorly known due to the high costs associated with sampling large oceanic areas. Top predators can be used as alternative low-cost samplers and indicators of the temporal variability of such systems. To study the variation in the composition of pelagic species through time in the broad Canary current region, we analysed foraging trips and regurgitations of Cory's shearwaters Calonectris borealis nesting on Selvagens islands, in 2008–2011 and 2016–2018. Fisheries data, oceanographic variables and the North Atlantic Oscillation were explored as possible explanatory variables for trends in behaviour and diet. Cory's shearwaters' diet, complemented by fisheries data, revealed marked changes in the composition of the pelagic fish communities. In 2016 there was a peak in the abundance of the Atlantic chub mackerel Scomber colias, followed by an explosive increase in the abundance of the Longspine snipefish Macroramphosus scolopax in 2017 and 2018, as deduced from the diet composition of the Cory's shearwater, and supported by fisheries data, in the broad oceanic area surrounding the Selvagens islands. Oceanographic variables did not show fluctuations correlated with these marked shifts in pelagic fish availability, the causes of which remain largely unknown. This study highlights the importance of the Atlantic chub mackerel and of the Longspine snipefish in the Madeira/Canary region and exemplifies the efficiency of avian predators in revealing rapid changes in pelagic communities of oceanic domains. Such trends and variations need to be better monitored and understood to measure the impact of ongoing global changes and to sustainably manage the marine environment and resources.

The purse-seine fishery for small pelagic fishes off the Madeira Archipelago

Small pelagic fishes constitute a valuable food resource for human consumption and are also important components of marine food webs. At Madeira, a Portuguese archipelago in the eastern Atlantic, they are the target of a year-round purse-seine fishery operating mainly off the south coast of Madeira Island. Landings of this fishery are mostly composed of blue jack mackerel Trachurus picturatus, Atlantic chub mackerel Scomber colias, and small amounts of sardine Sardina pilchardus. A fisheries observation programme was carried out, from October 2016 to December 2017, to quantify discards and slipping. Large differences were detected in the proportion of each species present in the landings and in the gross catches. Large amounts of the caught S. pilchardus (76.6%), S. colias (42.6%) and even T. picturatus (14.2%) were either discarded dead or slipped. Reasons for discarding included small sizes and a low market value obtained in the first sale of these species. The fishing pattern in this region is in striking contrast with that for mainland Portugal, where S. pilchardus is the most valuable small pelagic species, fetching a high market price. The results of this study suggest a need for the introduction of specific measures to promote more effective utilisation of the resources.

An overview of small-scale fisheries in the Northern Portuguese coast

An overview of small-scale fisheries in the Northern Portuguese coast

Seasonal evolution of small pelagic fish landings index in relation to oceanographic variables in the Canary Islands (Spain)

The main small pelagic fish species targeted by fishers in the Canary Islands are, in order of importance in landings: the Atlantic chub mackerel Scomber colias, horse mackerels Trachurus spp, the European pilchard Sardina pilchardus and sardinella Sardinella spp. In this study we evaluate seasonal relationships between selected oceanographic variables and these landings. Monthly values of Sea Surface Temperature (SST, °C), SST anomaly (SSTA, °C) and chlorophyll a concentration (Chl-a, mg/m3) were obtained for the study area between January 2009 and December 2016, and compared with the seasonal evolution of a landing index compiled from official sale notes. Non-parametric multivariate analyses enabled assessment of the seasonal variation of the catches over the study period. Despite strong interannual variability, different seasonal patterns were observed for each species, with cooler seasons (lower SST and higher Chl-a) characterized by catches of medium-sized species (S. colias and Trachurus spp), and warmer seasons (higher SST and lower Chl-a) by the smaller-sized species (S. pilchardus and Sardinella spp). SSTA appears to explain the unusual seasonal landings.

Feeding of pelagic fish in waters of Mauritania: 3.—Atlantic Chub mackerel Scomber colias, Atlantic horse mackerel Trachurus trachurus, Cunene horse mackerel Trachurus trecae

Feeding peculiarities of mass pelagic everyphagous fish Atlantic Chub mackerel Scomber colias, Atlantic horse mackerel Trachurus trachurus, Cunene horse mackerel Trachurus trecae from the Canary upwelling and the frontal zones of Mauritania were investigated. Atlantic Chub mackerel feeds mainly on fish inhabiting the zone of epipelagial, crustaceans and other organisms distributing in the sound scattering layers and also detritus and detritus–algal mixture. Cunene horse mackerel and Atlantic horse mackerel feed on mesopelagic fish and the organisms from the sound scattering layers. Feeding competition between these species does not occur due to non-concurrence of the places for concentration and nourishment. Correlation of food components, their occurrence and nourishment change for all species in conformity with fish sizes, physiological conditions and the season.

Disparate past demographic histories of three small Scombridae (Actinopterygii) species in Tunisian waters

The bullet tuna Auxis rochei, the little tunny Euthynnus alletteratus, and the Atlantic Chub mackerel Scomber colias are three small Scombridae with similar life-history traits such as overlapping epipelagic distribution and a shared spawning area in Tunisian waters. In this study, we compared the phylogeography and demographic histories of these species by analyzing the sequence variability of the mitochondrial DNA control region. None of the species showed genetic differentiation in their Tunisian distribution; however, we inferred three completely different population histories. E. alletteratus showed a demographic history of a very recent bottleneck followed by sudden population expansion probably consequence of a population decline in the Last Glacial Maximum. S. colias also presented a population expansion after collapse but in this case about ten-fold older than that observed in E. alletteratus. Finally, A. rochei presented a history of demographic stability. These contrasting population histories were discussed based on their possible differences in life-history traits, but the hypothesis of stochastic factors affecting the demography of these species was also invoked.