Analysis of Big Game Fishing Catches of Blue Marlin (Makaira nigricans) in the Madeira Archipelago (Eastern Atlantic) and Factors that Affect Its Presence

The archipelago of Madeira (Portugal) is one of the main European big game fishing locations, where the main target species is the blue marlin (Makaira nigricans). Catch data for these fish were used to analyze their presence over the years, estimate their average weights, and calculate annual fishing success rates. The results showed a marked seasonal effect, with higher average catch rates in summer (June–July), suggesting a migration from the equatorial waters they inhabit at the beginning of the year to northern areas when the waters become warmer. The influences of some environmental factors were analyzed using generalized additive models, and it was observed that the occurrence of blue marlin may be influenced by water temperature, wind, rain, and atmospheric pressure. This fishery did not register a high mortality rate in blue marlin specimens due to the usual practice of catch and release; individuals captured in this fishery can be used as a source of information that allows for follow-up on the status of the blue marlin population in the region.

Oil gland and oil pores in billfishes: in search of a function

ABSTRACTBillfishes are well known for their distinctive elongated rostra, i.e. bills. The functional significance of billfish rostra has been frequently discussed and the recent discovery of an oil gland (glandula oleofera) at the base of the rostrum in swordfish, Xiphias gladius, has added an interesting facet to this discussion regarding the potential co-evolution of gland and rostra. Here, we investigated the oil gland and oil pores (through which the oil is brought to the skin surface) of four billfish species – swordfish, Atlantic blue marlin (Makaira nigricans), Indo-Pacific sailfish (Istiophorus platypterus) and striped marlin (Kajikia audax) – and provide detailed evidence for the presence of an oil gland in the last three. All four species had a high density of oil pores on the forehead which is consistent with the hypothesis of hydrodynamic benefits of the oil. The extension of the pores onto the front half of the rostrum in sailfish and striped marlin, but not in swordfish or blue marlin, suggests that the oil may have additional functions. One such function could be linked to the antibacterial and anti-inflammatory properties of the oil. However, the available evidence on predatory rostrum use (and hence the likelihood of tissue damage) is only partly consistent with the extension of pores on rostra across species. We conclude that the oil gland probably serves multiple, non-mutually exclusive functions. More detailed information on rostrum use in blue marlin and swordfish is needed to better link behavioural and morphological data with the aim of accomplishing a full comparative analysis.

Density of the blue-black urchin Echinotrix diadema (Linnaeus, 1758) in Tomini Bay, Indonesia

The blue-black urchin has been widely known and utilized as food in the world, including Indonesia because sea urchin gonad can be consumed. However, the utilization of sea urchins in Gorontalo has not been performed. On the other hand, natural resources information is needed as the database for natural resources management in Tomini Bay. The aim of this study is to document the blue-black urchin Echinotrix diadema. This study conducted at Blue Marlin Beach, South Leato, Gorontalo, from November 2019 to December 2020. Sea urchin density was calculated with a 1 m × 1 m transect quadrate that positioned at interval 5 m in distance along 15 m of the transect line at the coral reef ecosystem. In parallel with the measurement of the density, sea urchin test diameter was measured with a Vernier caliper (0.01 mm accuracy), and the water temperature was measured with a thermometer. The results show that the average of sea urchin density is 3 ind. m–2 in November and December and 1 ind.m–2 in January. That density has no significant difference among the month. Moreover, the average size of the sea urchin test diameter is 60 mm in November, 63 mm in December, and 66 mm in January. The seawater temperature is 34 °C in November, 37 °C in December, and 33 °C in January. That results show that sea urchin density in the blue marlin beach is very low.

Incorporating depth into habitat use descriptions for sailfish Istiophorus platypterus and habitat overlap with other billfishes in the western North Atlantic

The sailfish Istiophorus platypterus is a circumglobal billfish species. It is commonly targeted in recreational fisheries and caught as by-catch in commercial fisheries, and therefore fisheries management would benefit from an enhanced understanding of basic patterns of the species’ daily and seasonal movements. Between 2002 and 2007, 87 billfish were tagged with pop-off satellite archival tags in the Atlantic waters off the coast of South Carolina, USA, including sailfish (n = 54), blue marlin Makaira nigricans (n = 15), and white marlin Kajikia albida (n = 18). Only fish meeting specific tag program criteria and length of tag attachment were selected for further analysis (sailfish, n = 19; blue marlin, n = 4; white marlin, n = 3). Differential horizontal and vertical movement patterns were observed within sailfish by season. Two- and three-dimensional (3D) analyses showed differential spatial niche use by sailfish. Among the istiophorid species, 3D analysis showed less overlap when occupying similar horizontal areas. The results from this study, in conjunction with similar studies from other areas, provide a better understanding of habitat usage that can be applied to address uncertainties in ecology or management, such as characterization of stock structure, identifying potential spawning habitat or intra-specific competition, providing correction factors for indices of abundance, and characterizing vulnerability to fishing gear.

Historical analysis of blue marlin (Makaira nigricans Lacepède, 1802) catches by the pelagic longline fleet in the eastern Pacific Ocean

We analysed a historical (1959–2017) database of blue marlin catches reported by the industrial pelagic longline fleet operating in the eastern Pacific Ocean. The time series of catch-per-unit-effort (CPUE) for the time period 1959–2015 was modelled as a function of temporal and environmental variables by using generalised additive mixed models (GAMM). CPUE predictions were made on an independent dataset (2016–2017). Results suggested that a higher nominal CPUE occurred near the equator during boreal winter, spring and autumn, with a shift towards the north during the boreal summer. Two high CPUE events were observed, one in the early 1960s and one in the early 1990s. The final GAMM explained 61% of the total variance of the CPUE time series. Only a small percentage of total deviance was explained by the environmental variables, so we suggest that changes in fleet-targeting practices are the main cause of the large variability in the time series. The final GAMM can be used to predict blue marlin CPUE with a prediction accuracy of 3–8 fish per 1000 hooks. We observed an important decline in CPUE from the early 2000s; the factors responsible for this decline should be further investigated.