scholarly journals Beyond Post-release Mortality: Inferences on Recovery Periods and Natural Mortality From Electronic Tagging Data for Discarded Lamnid Sharks

2021 ◽  
Vol 8 ◽  
Author(s):  
Heather D. Bowlby ◽  
Hugues P. Benoît ◽  
Warren Joyce ◽  
James Sulikowski ◽  
Rui Coelho ◽  
...  
Keyword(s):  
Survival Data ◽  
Recovery Period ◽  
Age Determination ◽  
Shark Species ◽  
Natural Mortality ◽  
The North ◽  
Covariate Effects ◽  
Shortfin Mako ◽  
Electronic Tagging ◽  
Key Parameter

Accurately characterizing the biology of a pelagic shark species is critical when assessing its status and resilience to fishing pressure. Natural mortality (M) is well known to be a key parameter determining productivity and resilience, but also one for which estimates are most uncertain. While M can be inferred from life history, validated direct estimates are extremely rare for sharks. Porbeagle (Lamna nasus) and shortfin mako (Isurus oxyrinchus) are presently overfished in the North Atlantic, but there are no directed fisheries and successful live release of bycatch is believed to have increased. Understanding M, post-release mortality (PRM), and variables that affect mortality are necessary for management and effective bycatch mitigation. From 177 deployments of archival satellite tags, we inferred mortality events, characterized physiological recovery periods following release, and applied survival mixture models to assess M and PRM. We also evaluated covariate effects on the duration of any recovery period and PRM to inform mitigation. Although large sample sizes involving extended monitoring periods (>90 days) would be optimal to directly estimate M from survival data, it was possible to constrain estimates and infer probable values for both species. Furthermore, the consistency of M estimates with values derived from longevity information suggests that age determination is relatively accurate for these species. Regarding bycatch mitigation, our analyses suggest that juvenile porbeagle are more susceptible to harm during capture and handling, that keeping lamnid sharks in the water during release is optimal, and that circle hooks are associated with longer recovery periods for shortfin mako.

Age and stock structure of gemfish (Rexea solandri) in New Zealand waters

1999 ◽  
Vol 50 (2) ◽  
pp. 103 ◽  
Author(s):  
P. L. Horn ◽  
R. J. Hurst
Keyword(s):  
Growth Parameters ◽  
Age Determination ◽  
Natural Mortality ◽  
Stock Structure ◽  
Von Bertalanffy ◽  
Length Frequency ◽  
Frequency Distributions ◽  
The North ◽  
Spawning Areas

Age determination of gemfish by counting hyaline zones in otoliths was validated by following the progression of modes in length–frequency distributions and the progression of strong and weak year classes in age–frequency distributions. Length–frequency and otolith samples were examined from four areas (west Northland, east Northland and Bay of Plenty, Wairarapa coast, and the Stewart- Snares shelf). Age–frequency distributions and von Bertalanffy growth parameters were calculated and compared between areas. Two gemfish stocks are indicated on the basis of patterns of year class strengths, trends in commercial landings and likely spawning areas; one off the east and north of the North Island, and another off the west and south of the South Island. Estimates of natural mortality are presented for the two stocks.

scholarly journals Bomb dating and age determination of large pelagic sharks

2002 ◽  
Vol 59 (3) ◽  
pp. 450-455 ◽  
Author(s):  
Steven E Campana ◽  
Lisa J Natanson ◽  
Sigmund Myklevoll
Keyword(s):  
Age Determination ◽  
Shark Species ◽  
Apex Predators ◽  
Age Validation ◽  
Growth Band ◽  
Shortfin Mako ◽  
Growth Bands ◽  
Bomb Radiocarbon ◽  
The 1960S ◽  
Vertebral Growth

Despite their notoriety and role as apex predators, the longevity of large pelagic sharks such as the porbeagle (Lamna nasus) and shortfin mako (Isurus oxyrinchus) is unknown. Vertebral growth bands provide an accurate indicator of age in young porbeagle, but age validation has never been reported for any large shark species past the age of sexual maturity. Here, we report the first application of bomb radiocarbon as an age validation method for long-lived sharks based on date-specific incorporation of radiocarbon into vertebral growth bands. Our results indicate that porbeagle vertebrae recorded and preserved a bomb radiocarbon pulse in growth bands formed during the 1960s. Through comparison of radiocarbon assays in young, known-age porbeagle collected in the 1960s with the corresponding growth bands in old porbeagle collected later, we confirm the validity of porbeagle vertebral growth band counts as accurate annual age indicators to an age of at least 26 years. The radiocarbon signatures of porbeagle vertebral growth bands appear to be temporally and metabolically stable and derived mainly from the radiocarbon content of their prey. Preliminary radiocarbon assays of shortfin mako vertebrae suggest that current methods for determining shortfin mako age are incorrect.

scholarly journals Atlantic Shortfin Mako: Chronicle of a Death Foretold?

Laws ◽  
2021 ◽  
Vol 10 (3) ◽  
pp. 52
Author(s):  
Mercedes Rosello ◽  
Juan Vilata ◽  
Dyhia Belhabib
Keyword(s):  
North Atlantic ◽  
Law Of The Sea ◽  
Commercial Fishing ◽  
Shark Species ◽  
Applicable Law ◽  
Incidental Capture ◽  
The North ◽  
Isurus Oxyrinchus ◽  
Shortfin Mako ◽  
Ocean Region

This article outlines recent events concerning the conservation and management trajectory of a highly migratory shark species, the shortfin mako (Isurus oxyrinchus), in the North Atlantic, where it has been routinely captured recreationally and as part of commercial fishing operations alongside other species. Noting recent warnings concerning the high mortality of the species in this ocean region, and the threat of imminent population collapse, this article sets out a number of applicable law of the sea provisions, and carries out an evaluation of relevant measures for target and incidental capture species, discussing their applicability to the mako fishery. It also presents an analysis of regional and global governance actions taken to date by the international community and by individual actors, noting a number of shortfalls, and outlining potential responses.

scholarly journals Movements, Habitat Use, and Diving Behavior of Shortfin Mako in the Atlantic Ocean

2021 ◽  
Vol 8 ◽  
Author(s):  
Catarina C. Santos ◽  
Andrés Domingo ◽  
John Carlson ◽  
Lisa J. Natanson ◽  
Paulo Travassos ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
Habitat Use ◽  
Diving Behavior ◽  
Shark Species ◽  
Depth Range ◽  
Southwest Atlantic ◽  
Vertical Movements ◽  
The North ◽  
Management Measures ◽  
Shortfin Mako

The shortfin mako is one of the most important shark species caught in Atlantic Ocean pelagic fisheries. Given increasing concerns for the stock status of the species, the present study was designed to fill gaps in the knowledge of habitat use and movement patterns of shortfin mako in the Atlantic Ocean. From 2015 to 2019, 53 shortfin makos were tagged with pop-up satellite archival tags within the North, Central, and Southwest Atlantic Ocean, with successful transmissions received from 34 tags. Generally, sharks tagged in the Northwest and Central Atlantic moved away from tagging sites showing low to no apparent residency patterns, whereas sharks tagged in the Northeast and Southwest Atlantic spent large periods of time near the Canary Archipelago and Northwest Africa, and over shelf and oceanic waters off southern Brazil and Uruguay, respectively. These areas showed evidence of site fidelity and were identified as possible key areas for shortfin mako. Sharks spent most of their time in temperate waters (18–22°C) above 90 m; however, data indicated the depth range extended from the surface down to 979 m, in water temperatures ranging between 7.4 and 29.9°C. Vertical behavior of sharks seemed to be influenced by oceanographic features, and ranged from marked diel vertical movements, characterized by shallower mean depths during the night, to yo-yo diving behavior with no clear diel pattern observed. These results may aid in the development of more informed and efficient management measures for this species.

scholarly journals Spatiotemporal variation in size-structured populations using fishery data: an application to shortfin mako (Isurus oxyrinchus) in the Pacific Ocean

2017 ◽  
Vol 74 (11) ◽  
pp. 1765-1780 ◽  
Author(s):  
Mikihiko Kai ◽  
James T. Thorson ◽  
Kevin R. Piner ◽  
Mark N. Maunder
Keyword(s):  
Coastal Waters ◽  
Mixed Model ◽  
Linear Mixed Model ◽  
Marine Species ◽  
Structured Populations ◽  
Spatiotemporal Model ◽  
The North ◽  
Isurus Oxyrinchus ◽  
Shortfin Mako ◽  
Catch Rates

We develop a length-disaggregated, spatiotemporal, delta-generalized linear mixed model (GLMM) and apply the method to fishery-dependent catch rates of shortfin mako sharks (Isurus oxyrinchus) in the North Pacific. The spatiotemporal model may provide an improvement over conventional time-series and spatially stratified models by yielding more precise and biologically interpretable estimates of abundance. Including length data may provide additional information to better understand life history and habitat partitioning for marine species. Nominal catch rates were standardized using a GLMM framework with spatiotemporal and length composition data. The best-fitting model showed that most hotspots for “immature” shortfin mako occurred in the coastal waters of Japan, while hotspots for “subadult and adult” occurred in the offshore or coastal waters of Japan. We also found that size-specific catch rates provide an indication that there has been a recent increasing trend in stock abundance since 2008.

Modeling population dynamics and nonstationary processes of difficult-to-age fishery species with a hierarchical Bayesian two-stage model

2019 ◽  
Vol 76 (12) ◽  
pp. 2199-2214 ◽  
Author(s):  
Yan Li ◽  
Laura M. Lee ◽  
Jason Rock
Keyword(s):  
North Carolina ◽  
Population Dynamics ◽  
Natural Mortality ◽  
Hierarchical Bayesian ◽  
Stage Model ◽  
Survey Analysis ◽  
Two Stage ◽  
The North ◽  
Fishery Species

Modeling population dynamics and establishing a comprehensive population assessment for fishery species that are difficult to age have been challenging. Determination of age for such species is still an unresolved issue or is at best uncertain. Catch-survey analysis does not require full age information but can still provide a comprehensive population assessment. It was extended to incorporate multiple surveys and multiple sources of uncertainties within the statistical catch-at-age framework in the applications to crustaceans. Here, we further generalize and extend the multiple survey catch-survey analysis into a hierarchical Bayesian two-stage model by applying the hierarchical Bayesian approach. The hierarchical Bayesian approach can sufficiently incorporate uncertainty and expert opinions in parameter estimation. We developed a series of models with different assumptions for natural mortality and catchability, including nonstationary (i.e., time-varying) assumptions. We evaluated model robustness to these assumptions and compared population dynamics estimates and population status determination. We demonstrated the application of the hierarchical Bayesian two-stage model using the North Carolina blue crab (Callinectes sapidus) example. In this example, estimation of population size and fishing mortality and determination of population status were robust to the natural mortality and catchability assumptions. The North Carolina blue crab population is less likely to have nonstationary catchability or nonstationary natural mortality. Its natural mortality is more likely to vary by stage than by sex or over time.

Further studies on age and trypanosome infection rates in Glossina pallidipes Aust., G. palpalis fuscipes Newst. and G. brevipalpis Newst. in Uganda

1967 ◽  
Vol 57 (3) ◽  
pp. 459-477 ◽  
Author(s):  
J. M. B. Harley
Keyword(s):  
Infection Rate ◽  
Lake Victoria ◽  
Age Determination ◽  
Glossina Pallidipes ◽  
Physiological Age ◽  
Developmental Cycle ◽  
Seasonal Fluctuations ◽  
The North ◽  
North Eastern ◽  
The Mean

Between June 1964 and May 1965, samples of Glossina pallidipes Aust., G. palpalis fuscipes Newst. and G. brevipalpis Newst. were caught in an area on the north-eastern shore of Lake Victoria in Uganda. Both males and females were classified into age-categories according to the degree of wear of the wings. Females were also classified into ovarian age-categories according to the exact or approximate number of ovulations that had taken place. All were examined for presence of infections with Trypanosoma, which were classified as vivax-type, congolense-type or brucei-type according to their location in the flies.The percentage compositions of the samples by wing-fray category are compared. The mean wing-fray category of females of G. palpalis fuscipes and G. brevipalpis was somewhat lower, and that of females of G. pallidipes somewhat higher, than that of the corresponding males. However, the figures for infection rate in females of all three species were higher than in the corresponding males, significantly so in G. pallidipes and G. palpalis fuscipes, and it seems probable that the mean age of females, at least of the two latter species, was greater than that of males. Among females, the range of calendar ages of flies in the various fray categories was wide.The physiological age-determination method, in which females older than about 42 days are classified iDto four age-categories, does not extend sufficiently far to give a reasonable pattern for the age-composition of any of the species at Lugala, and many of the individuals caught must have been more than about 80 days old.Seasonal fluctuations in mean wing-fray and in the proportion of old flies in the population were correlated with changes in infection rate of females of G. palpalis fuscipes but not of females of G. pallidipes. Among males of neither species were seasonal fluctuations in mean fray correlated with changes in infection rate, though among those of G. palpalis fuscipes the two varied similarly between June and February.Females of G. pallidipes and G. palpalis fuscipes about 31–42 days old had significantly fewer brucei-type infections than those over 42 days old, and either the developmental cycle in the field must normally be longer than that recorded in laboratory investigations or many of the flies must become infected when more than just a few days old.

Enumerating Populations of Adults of the Red Locust, Nomadacris septemfasciata (Serville), in its Outbreak Areas in East and Central Africa

1958 ◽  
Vol 49 (2) ◽  
pp. 273-285 ◽  
Author(s):  
C. C. Scheepers ◽  
D. L. Gunn
Keyword(s):  
Total Population ◽  
Central Africa ◽  
Nomadacris Septemfasciata ◽  
Natural Mortality ◽  
Red Locust ◽  
Frequency Distributions ◽  
Moving Vehicle ◽  
The North ◽  
Outbreak Area ◽  
Outbreak Areas

SummaryA method is described of estimating the total numbers and frequency distributions of adults of the Red Locust, Nomadacris septemfasciata (Serv.), in outbreak areas of hundreds of square miles, based upon counting the numbers that fly up in a two-yard strip in front of a moving vehicle. The method has proved itself valuable for indicating both immediate and future requirements for killing the locusts, but it requires refining for some research purposes.By this method, the importance has been clearly shown of the process of congregation of scattered adult locusts in forming emigrant swarms that could start a plague. The locusts do not congregate but actually disperse just before laying eggs.The total population in part (189 sq. miles) of the North Rukwa Outbreak Area (a self-contained area of 253 sq. miles) in Tanganyika Territory has been followed for four years. There are indications that a small migrant swarm contains 5–10 million locusts, that a total population in the whole of the North Rukwa Outbreak Area of 20 million locusts is unlikely to yield a migrant swarm, but that 50 million locusts could readily do so.In 1953, after poor rains, no natural mortality was detected between July and October by the assessment methods described. In 1957, after good rains, natural mortality of 70–90 per cent. was revealed by the same methods, although the dry season was not fully covered by the assessments.

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