Sexual size dimorphism, spatial segregation and sex-biased bycatch of southern and northern royal albatrosses in pelagic longline fisheries

AbstractBycatch in longline fisheries is a major contributor to the global decline of albatrosses. Sexual segregation at sea often leads to unequal overlap with different fisheries, resulting in sex-biased bycatch, exacerbating the impact on a population level. In great albatrosses (Diomedea spp.), males (the larger sex) tend to spend more time at higher latitudes than females, attributed to competitive exclusion or differences in flight performance mediated by the pronounced sexual size dimorphism (SSD). Consequently, larger numbers of females are bycaught in pelagic longline fisheries in subtropical and temperate areas. Although this has been shown for Diomedea exulans, it has not been confirmed for all great albatross species. Here we examined the degree of SSD and developed discriminant functions to determine species and sex in D. epomophora and D. sanfordi; species that are often killed in several fisheries in the Southern Hemisphere. Based on a large sample of albatrosses bycaught off Uruguay, both species showed substantial SSD. Discriminant functions assigned species and sex to otherwise indeterminate individuals with 90–100% accuracy. Based on all birds identified (n=128), bycatch in the pelagic longline fishery was female-biased, indicating sexual segregation at sea. The discriminant functions presented enable species and sex to be identified, providing critical data for future bycatch assessments.

Download Full-text

Evolution of sexual size dimorphism and sexual segregation in artiodactyls: the chicken or the egg?

Mammalian Biology ◽

10.1007/s42991-021-00193-4 ◽

2021 ◽

Author(s):

Marcelo H. Cassini

Keyword(s):

Sexual Size Dimorphism ◽

Sexual Segregation ◽

Size Dimorphism

Download Full-text

Analysis of marine mammal bycatch in the Uruguayan pelagic longline fishery operating in the Southwestern Atlantic Ocean

ICES Journal of Marine Science ◽

10.1093/icesjms/fsu250 ◽

2015 ◽

Vol 72 (5) ◽

pp. 1637-1652 ◽

Cited By ~ 6

Author(s):

Cecilia Passadore ◽

Andrés Domingo ◽

Eduardo R. Secchi

Keyword(s):

Atlantic Ocean ◽

Marine Mammals ◽

Population Decline ◽

Additive Models ◽

Longline Fishery ◽

Southwestern Atlantic ◽

Southwestern Atlantic Ocean ◽

Pelagic Longline Fishery ◽

The Impact ◽

Pelagic Longline

Abstract Bycatch is one of the main causes of human-caused mortality and population decline of many marine mammals. Monitoring bycatch is the first step to understand the impact of the fisheries on the species affected. Understanding how the interaction between marine mammals and fishing operations varies in space and time, and how it is influenced by environmental variables, is essential for designing mitigation strategies to reduce bycatch mortality. In this paper, we use data gathered by scientific observers and a fishing skipper to analyse marine mammals bycatch by the Uruguayan pelagic longline fishery operating in the Southwestern Atlantic Ocean from 1996 to 2007. The total bycatch per unit effort (Bcpue) was 0.0150 marine mammals/1000 hooks and the highest values (∼0.2) were recorded between 37°–38°S and 49°–51°W. Total cetacean Bcpue during the study period was low (0.0051 cetacean/1000 hooks) and occurred between 32°–37°S and 46°–54°W. Generalized additive models showed that cetaceans' bycatch was mainly affected by the depth, sea surface temperature, and season. Although cetaceans were captured year-round, the highest values were registered in spring months, most bycatch events occurred over the continental slope (median = 619 m) and in waters with a median temperature of 19.7°C. The bycatch of pinnipeds was influenced by depth, location, and season. Pinniped bycatch occurred mainly in winter, in waters ranging from 80 to 5000 m of depth (median = 2366 m) between 34°–37°S (median = 35.9°S) and 54°–49°W (median = 51.8°W). The spatial analysis showed that most bycatch events occurred within the Brazil–Malvinas Confluence zone, an area of high productivity where the pelagic longline fleet concentrates its fishing effort and where marine mammals probably concentrate to feed.

Download Full-text

Sexual size dimorphism in relation to age and growth based on skeletochronological analysis in a Tibetan frog

Amphibia-Reptilia ◽

10.1163/156853809788795155 ◽

2009 ◽

Vol 30 (3) ◽

pp. 351-359 ◽

Cited By ~ 14

Author(s):

Xin Lu ◽

Xiaoyan Ma

Keyword(s):

Growth Rate ◽

Cross Sections ◽

Sexual Difference ◽

Sexual Size Dimorphism ◽

Population Level ◽

Age And Growth ◽

Size Difference ◽

Size Dimorphism ◽

Asymptotic Size ◽

Central Tibet

AbstractThe number of lines of arrested growth (LAGs) in diaphyseal cross-sections of phalanges or femora was used to assess individual age and growth of 612 Nanorana parkeri, including 363 males, 143 females, 70 juveniles, and 36 tadpoles, in a population from central Tibet, China. The oldest immature frogs had an age of 6 years; both the youngest sexually mature males and females were 3 years old. However, the majority of individuals bred for the first time at 5 years in males and 6 years in females. Females had greater average age (6.27 years) and lifespan (11 years) than males (5.72 and 10 years). At the population level, females, on average, were significantly larger in body length (40.3 mm) than males (37.0 mm). However, the significant size difference only occurred when both sexes were over 6 years old, at which most frogs attained maturity. Growth curve and growth rate estimated for each sex based on a von Bertalanffy model showed that females had a larger asymptotic size (54.2 mm) but smaller growth coefficient k (0.16) than males (40.0 mm, 0.37), and that females had greater growth rate than males in all age classes, except at metamorphosis. According to these results, we concluded that the sexual difference of growth between pre- and post-maturation periods contributed to the age-specific sexual size dimorphism of N. parkeri.

Download Full-text

The Evolution of Female-Biased Sexual Size Dimorphism: A Population-Level Comparative Study in Horned Lizards (Phrynosoma)

Evolution ◽

10.2307/2411352 ◽

1998 ◽

Vol 52 (6) ◽

pp. 1821 ◽

Cited By ~ 37

Author(s):

Kelly R. Zamudio

Keyword(s):

Comparative Study ◽

Sexual Size Dimorphism ◽

Population Level ◽

Size Dimorphism ◽

Horned Lizards

Download Full-text

A Comparison of Alternative Circle Hook (Kahle Hook) and J Style Hook Performance in Experimental Pelagic Longline Fishery in Turkey

Turkish Journal of Fisheries and Aquatic Sciences ◽

10.4194/1303-2712-v15_1_03 ◽

2015 ◽

pp. 19-27 ◽

Cited By ~ 1

Author(s):

Aytaç Özgül ◽

Ali Ulaş ◽

Altan Lök ◽

F. Ozan Düzbastılar ◽

Cengiz Metin

Keyword(s):

Longline Fishery ◽

Fish Catch ◽

Study Circle ◽

The Difference ◽

Pelagic Longline Fishery ◽

By Catch ◽

Catch Rates ◽

Longline Fisheries ◽

Marine Wildlife ◽

Pelagic Longline

In recent years, circle hooks have been encouraged as an alternative to traditional J-hooks in pelagic longline fisheries to minimize by-catch mortality and injury to sea turtles and other marine wildlife. Prior to this study, circle hooks had not been used by domestic commercial pelagic longliners in Turkey. The main objective of the study was to evaluate the efficiency of kahle hook comparing with J-style hook baited with sardine (Sardina pilchardus) in pelagic longline fishery in the Aegean coast of Turkey (Kuşadası Bay).We used conventional J-style hooks (Mustad 2315DT-4/0) and kahle hooks (Eagle Claw142A-6/0) for each fishing operation and compared catch rates, catch compositions of target and non-target species. The relative performance of kahle and traditional J-style hooks was tested during 22 valid pelagic longline fishing operations between August 2010 and December 2012. A total of 2200 hooks were used equally amongkahle and J-style hooks consecutively. Captured fish were identified, total and fork lengths were measured,weighed, the time of haulback, and hook type as well as by-catch fish were recorded. A total of 78 fish were caught belonging to 13 species during the samplings. The overall CPUE was 4.73 fishes per 100 hooks for kahle hooks and 2.46 fishes for J-style hooks. For the CPUE of all fishes, the difference was statistically significant (Z = -1.977; P<0.05), in favour of the kahle hook being almost two times greater than the J-style hook. Likewise CPUE was 17007.69 g per 100 hooks for kahle style hooks and 4807.27 g for J-style hooks (Z = -1.997; P<0.05). While no difference was found between two hook models on by-catch species, kahle hooks were more efficient in comparison to J hooks on discard species. Swordfish (Xiphiasgladius) had the highest CPUE (2.82) among all species for kahle hooks followed by silver scabbard fish (Lepidopuscaudatus), 0.64. For J-style hooks, silver scabbard fish catch had the highest CPUE (0.64) followed by swordfish (0.55).

Download Full-text