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"Blue marlin."
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Global habitat loss of a highly migratory predator, the blue marlin (Makaira nigricans)
Aim Climate change is driving the redistribution of species throughout the oceans. However, the speed and magnitude of species responses, including shifts in their distribution, are variable and species specific. Quantifying the effect of environmental conditions on species distributions is crucial to informing management and conservation efforts. Blue marlin (Makaira nigricans) is a wide‐ranging top predator occurring circumglobally in tropical and subtropical waters and is heavily impacted by international longline fisheries. This study aimed to predict the global distribution of blue marlin and characterize the effects of climate variability thereon. Location Global. Methods To conduct this study, pop‐up satellite archival tags (n = 144) deployed by recreational anglers through a global citizen science programme were used to generate a large tracking data set (14,928 days, 210,983 km from deployment to pop‐up locations) of blue marlin movement across three ocean basins. State‐space modelled tracking position estimates were used to create a species distribution model to represent global habitat suitability for blue marlin. Habitat suitability was determined by fitting a generalized additive mixed model (GAMM) as a function of environmental covariates which was used to predict monthly global blue marlin habitat from 2000 to 2016. Results Blue marlin habitat preference had the strongest association with sea surface temperature. Seasonal variation in blue marlin habitat occurs primarily at the latitudinal edges of the distribution range. Over the duration of the study, 96% of core habitat declined in suitability, with a concurrent poleward increase in suitability of marginal habitat. Main Conclusions This study highlights the successful application of citizen‐based science to develop a long‐term global telemetry dataset. The present‐day loss of highly suitable habitat suggests ocean warming may be making equatorial waters less suitable even to highly mobile species. Blue marlin is likely to respond by following preferred habitat as it shifts poleward.
Journal Article
Modeling the dynamic habitats of mobile pelagic predators (Makaira nigricans and Istiompax indica) in the eastern Pacific Ocean
Overexploitation and climate change can reduce the abundance and shift the spatial distribution of marine species. Determining the habitat suitability of a mobile pelagic species, such as blue marlin (BUM) Makaira nigricans and black marlin (BAM) Istiompax indica, can help describe their spatiotemporal distribution patterns over a broad spatial scale, which is crucial for fisheries management. We applied a species distribution model (MaxEnt) to model the dynamic suitable habitat of BUM and BAM using 14 yr (1997–2010) of Inter-American Tropical Tuna Commission occurrence data (n = 20 348) from purse-seine vessels in the eastern Pacific Ocean (EPO) and high-resolution remotely sensed oceanographic data. The spatial distribution of suitable habitat for both species varied seasonally and in response to El Niño–Southern Oscillation (ENSO), with BUM positively correlated with chlorophyll ₐ (chl ₐ) concentrations and sea surface temperature and BAM with chl ₐ concentrations and sea surface height. The influence of these environmental variables shifted seasonally suitable habitat between coastal (winter and spring) and oceanic (summer and fall) waters. During La Niña events, suitable habitat was along the equator, while during El Niño, suitable habitat shifted to farther northern and southern waters of the EPO. Analyses on species’ centers of suitable habitat (CSH) revealed that the strength of ENSO did not influence CSH; however, large displacements were observed during these events. The models applied in our study provide critical information on the spatiotemporal patterns of 2 mobile pelagic predators, which can potentially be used to forecast future distributions and develop effective management strategies in response to climate change.
Journal Article
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 popoff 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.
Journal Article
Vertical habitat use of Atlantic blue marlin Makaira nigricans: interaction with pelagic longline gear
We characterized Atlantic blue marlin Makaira nigricans temperature- depth vertical habitat utilization from data collected using 51 electronic pop-up satellite archival tags (PSATs) attached to fish released by recreational and commercial fishers. Most source data were in the form of 3 or 6 h, temperature- and depth-frequency histograms transmitted by the tags to the ARGOS satellite system. However, high resolution time series of temperatures, depths (30 or 60 s resolution), and light intensity were obtained from 6 tags that were physically recovered. The distributions of times at depth were significantly different between day and night. During daylight hours, the fish were typically below the near-surface layer, often at 40 to >100 m, sometimes remaining below the near-surface layer at depth throughout the daylight hours, but often returning briefly to the surface. At night, the fish spent most of their time at or very close to the surface. This pattern of behavior also meant that the distributions of time at temperature were significantly different between day and night, with the fish occupying warmer strata during darkness. We evaluated the fractions of time spent by each fish within each degree of water temperature relative to the temperature of the surface mixed layer to assess assumptions used to model population abundance trends from pelagic longline catch per unit effort (CPUE) data. Frequency distributions were determined for periods of darkness, daylight and, where possible, twilight. Results were highly variable within the time series for individual fish and among individuals. Assumptions about habitat usage in previous CPUE analyses are clearly inappropriate and may lead to serious errors that can propagate through the fisheries management system.
Journal Article
Mercury in the Blue Marlin (Makaira nigricans) from the Southern Gulf of California: Tissue Distribution and Inter-Annual Variation (2005–2012)
With the aim of knowing annual variations of Hg concentrations in muscle and liver of blue marlin (
Makaira nigricans
) from the southern Gulf of California, fish were collected between 2005 and 2012 in three areas. In general, Hg levels were more elevated in liver than in muscle. Variations of Hg concentrations in muscle and liver among the studied years were not significant. Hg levels in muscle and liver increased significantly with length and weight of fish. In comparison to other studies, Hg levels in muscle and liver were lower. With respect to maximum permissible limits (1.0 µg g
−1
wet weight) of Hg in Mexico, the average concentration (1.91 µg g
−1
wet weight) in the edible portion (muscle) of blue marlin was over the legal limit; this issue is worth research efforts in relation to the rate of ingestion of this species and the co-occurrence of selenium in the edible portion.
Journal Article
Sex-structured population dynamics of blue marlin Makaira nigricans in the Pacific Ocean
The population dynamics of the blue marlin
Makaira nigricans
stock in the Pacific Ocean were estimated for 1971–2011 using a fully integrated length-based, age-, and sex-structured model. Fishery-specific catch, size composition, and catch-per-unit of effort were used in the modeling as likelihood components. Estimated dynamics were consistent with a stock that is fully exploited and stable over the last several years. No significant trends in recruitment were noted; however, female blue marlin were estimated to make up a majority of the catch, and historical exploitation has disproportionately changed the age structure of females relative to males. This result is due to differences in assumed life history and estimated selectivity. Changes to important life history parameters that are responsible for the productivity of the stock would potentially change the interpretation of current stock status.
Journal Article
Reproductive biology of blue marlin Makaira nigricans around Yonaguni Island, southwestern Japan
We studied the spawning seasonality and gonadal development of blue marlin
Makaira nigricans
using specimens captured around Yonaguni Island in southwestern Japan between February 2003 and February 2006. The mean (±SD) lower jaw–fork length of females (234 ± 24 cm) was greater than that of males (191 ± 12 cm). The smallest mature female and male were 183 and 160 cm, respectively. Most of the 717 females had immature ovaries. However, in March and from May to September, the ovaries of 26 females contained oocytes with yolk globules, hydrated oocytes, or postovulatory follicles. Most males had testes with a large amount of spermatozoa throughout the year. The occurrence of mature blue marlin at Yonaguni Island suggests that spawning occurs here. The mean condition factors (fatness of the fish) of both sexes decreased from March to June or July, presumably as they expended energy to reproduce. We discuss our results in the context of migration theory for blue marlin in the western North Pacific Ocean.
Journal Article
Ocean vet. 4, The blue marlin
Narrated by Hollywood legend Michael Douglas, Ocean Vet follows the exploits of veterinarian Dr. Neil Burnie and his Ocean Vet team. Together they set out to save, protect, and learn more about Bermuda’s incredible marine life. Neil expands his veterinary knowledge and tests his fishing skills to their limit in one of the teams most exciting adventures. Watch as Neil and the Ocean Vet team wrestle a monster blue marlin to the side of the boat to attach a satellite tag that will expand the scientific knowledge of this species by revealing its oceanic migrations. Follow Neil and his team as they dissect a giant blue marlin donated to them by a local fishing tournament. Neil and his team expand their knowledge and understanding of the anatomical and evolutionary wonders that make this animal one of the fastest and most formidable predators in the ocean.
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