The rostral micro-tooth morphology of blue marlin, Makaira nigricans.

Billfish rostra potentially have several functions; however, their role in feeding is unequivocal in some species. Recent work linked morphological variation in rostral micro-teeth to differences in feeding behavior in two billfish species, the striped marlin (Kajikia audax) and the sailfish (Istiophorus platypterus). Here, we present the rostral micro-tooth morphology for a third billfish species, the blue marlin (Makaira nigricans), for which the use of the rostrum in feeding behavior is still undocumented from systematic observations in the wild. We measured the micro-teeth on rostrum tips of blue marlin, striped marlin, and sailfish using a micro-computed tomography approach and compared the tooth morphology among the three species. This was done after an analysis of video-recorded hunting behavior of striped marlin and sailfish revealed that both species strike prey predominantly with the first third of the rostrum, which provided the justification to focus our analysis on the rostrum tips. In blue marlin, intact micro-teeth were longer compared to striped marlin but not to sailfish. Blue marlin had a higher fraction of broken teeth than both striped marlin and sailfish, and broken teeth were distributed more evenly on the rostrum. Micro-tooth regrowth was equally low in both marlin species but higher in sailfish. Based on the differences and similarities in the micro-tooth morphology between the billfish species, we discuss potential feeding-related rostrum use in blue marlin. We put forward the hypothesis that blue marlin might use their rostra in high-speed dashes as observed in striped marlin, rather than in the high-precision rostral strikes described for sailfish, possibly focusing on larger prey organisms.

Lacunae rostralis: A new structure on the rostrum of sailfish Istiophorus platypterus.

Recent comparative studies of billfishes (Istiophoridae and Xiphiidae) have provided evidence of differences in the form and function of the rostra (bill) among species. Here, we report the discovery of a new structure, lacuna rostralis, on the rostra of sailfish Istiophorus platypterus, which is absent on the rostra of swordfish Xiphias gladius, striped marlin Kajikia audax and blue marlin Makaira nigricans. The lacunae rostralis are small cavities that contain teeth. They were found on the ventral rostrum surface of all I. platypterus specimens examined and dorsally in half of them. Ventrally, the lacunae rostralis were most prominent in the mid-section of the rostrum. Dorsally, they occurred closer to the tip. The density of lacunae rostralis increased towards the rostrum tip but, because they are smaller in size, the percentage of rostrum coverage decreased. The teeth located within the lacunae rostralis were found to be different in size, location and orientation from the previously identified micro-teeth of billfish. We propose two potential functions of the lacunae rostralis that both relate to the use of the bill in feeding: mechanoreception of prey before tapping it with the bill and more efficient prey handling via the creation of suction, or physical grip.

Tunabio: biological traits of tropical tuna and bycatch species caught by purse seine fisheries in the Western Indian and Eastern Central Atlantic Oceans.

Background: Along with the development of the tropical tuna purse-seine fishery from the 1960s in the Atlantic Ocean and from the 1980s in the Indian Ocean, many projects and studies have been conducted to improve knowledge about the biology, migrations and dynamics of the stocks of target and non-target (i.e. bycatch) species taken in these fisheries. Since the 2000s, the European Union (EU) has been supporting Member States in the collection of biological data on species caught by their purse seine and pole and line fisheries, thus making it possible to have a long-term series of data. Biological data have never been saved by the different tuna commissions, unlike the catches by species and sizes by areas and periods. However, these data are essential to monitor the status of the fisheries and fuel the assessment models used by the tuna Regional Fisheries Management Organisations (tRFMOs) for the sustainable management and conservation of the fish stocks under their mandate. New information: We combined historical (1974-1999) and current (2003-2020) datasets on the biology of tropical tunas and bycatch fish caught by large-scale purse seiners in the Eastern Atlantic Ocean (EAO) and Western Indian Ocean (WIO). The resulting Tunabio database is presented in the present data paper and contains all available morphometric and biological data collected on more than 80,000 fish individuals.

Northeast Arctic cod population persistence in the Lofoten-Barents Sea system under fishing.

Population growth, and hence the population's persistence, is affected by several factors such as climate, species interaction, and harvesting pressure. Proper resource management requires an understanding of these factors. We apply techniques based upon age-structured population matrices to analyze estimated stock sizes derived from annual bottom trawl sampling in the winter feeding area of northeast Arctic cod (Gadus morhua L.) from 1981 to 2003. We run generalized additive models to explain population growth rate by different explanatory variables. Cod population growth was found to be positively related to the abundance of capelin (Mallotus villosus Miller), negatively related to the number of cannibalistic cod with a two-year lag, and marginally positively related to the winter North Atlantic Oscillation index (NAO). This model remains true independently from the population status (i.e., fished or non-fished). Capelin abundance is the main variable that to some degree can be adjusted in order to maintain the population size at a given level of cod harvesting. Our results point to the importance of managing conjointly cod and capelin stocks.

Toothed whale and shark depredation indicators: A case study from the Reunion Island and Seychelles pelagic longline fisheries.

Depredation in marine ecosystems is defined as the damage or removal of fish or bait from fishing gear by predators. Depredation raises concerns about the conservation of species involved, fisheries yield and profitability, and reference points based on stock assessment of depredated species. Therefore, the development of accurate indicators to assess the impact of depredation is needed. Both the Reunion Island and the Seychelles archipelago pelagic longline fisheries targeting swordfish (Xiphias gladius) and tuna (Thunnus spp.) are affected by depredation from toothed whales and pelagic sharks. In this study, we used fishery data collected between 2004 and 2015 to propose depredation indicators and to assess depredation levels in both fisheries. For both fisheries, the interaction rate (depredation occurrence) was significantly higher for shark compared to toothed whale depredation. However, when depredation occurred, toothed whale depredation impact was significantly higher than shark depredation impact, with higher depredation per unit effort (number of fish depredated per 1000 hooks) and damage rate (proportion of fish depredated per depredated set). The gross depredation rate in the Seychelles was 18.3%. A slight increase of the gross depredation rate was observed for the Reunion Island longline fleet from 2011 (4.1% in 2007-2010 and 4.4% in 2011-2015). Economic losses due to depredation were estimated by using these indicators and published official statistics. A loss of 0.09 EUR/hook due to depredation was estimated for the Reunion Island longline fleet, and 0.86 EUR/hook for the Seychelles. These results suggest a southward decreasing toothed whale and shark depredation gradient in the southwest Indian Ocean. Seychelles depredation levels are among the highest observed in the world revealing this area as a "hotspot" of interaction between pelagic longline fisheries and toothed whales. This study also highlights the need for a set of depredation indicators to allow for a global comparison of depredation rates among various fishing grounds worldwide.