Reevaluating evidence of density-dependent growth in northern fur seals (Callorhinus ursinus) based on measurements of archived skeletal specimens

2004 ◽  
Vol 61 (9) ◽  
pp. 1616-1626 ◽  
Author(s):  
Michael A Etnier
Keyword(s):  
Growth Rates ◽  
Environmental Conditions ◽  
Somatic Growth ◽  
Callorhinus Ursinus ◽  
Density Dependent ◽  
Fur Seals ◽  
Time Period ◽  
Northern Fur Seals ◽  
Time Periods ◽  
Dependent Growth

Analysis of length-at-age measurements of archived skeletal material shows that somatic growth rates of male northern fur seals (Callorhinus ursinus) vary inversely with population density. Von Bertalanffy growth curves were estimated for two series of known-age mandibles collected 1911–1920 (n = 156) and 1940–1953 (n = 151), time periods representing the historic population minimum and maximum, respectively. Mandibles from the former time period are larger than mandibles from the latter time period, suggesting a density-dependent response in somatic growth. Although density-dependent growth in northern fur seals has been suggested before, previous studies have been hampered by the potentially confounding factors of fisheries interactions, variable environmental conditions, and harvest of adult female northern fur seals. The material analyzed here pre-dates the substantial development of the Bering Sea groundfish fishery and the period of heaviest culling of females. Likewise, the two time periods examined are characterized by broadly similar climatic and environmental conditions. Therefore, the results support the hypothesis that measurements of somatic growth rates provide an index of population levels relative to carrying capacity. Growth rate studies could therefore be used to evaluate the current population status of northern fur seals.

Estimation of Sexual Maturity Based on Morphometrics of Genital Organs in Male Northern Fur Seals, Callorhinus ursinus

Mammal Study ◽  
2020 ◽  
Vol 46 (1) ◽  
Author(s):  
Yukino Hirakawa ◽  
Takanori Horimoto ◽  
Ippei Suzuki ◽  
Yoko Mitani
Keyword(s):  
Sexual Maturity ◽  
Callorhinus Ursinus ◽  
Fur Seals ◽  
Northern Fur Seals

NATURALLY-OCCURRING LEPTOSPIROSIS IN NORTHERN FUR SEALS (Callorhinus ursinus)

1977 ◽  
Vol 13 (2) ◽  
pp. 144-148 ◽  
Author(s):  
ALVIN W. SMITH ◽  
RICHARD J. BROWN ◽  
DOUGLAS E. SKILLING ◽  
H. L. BRAY ◽  
MARK C. KEYES
Keyword(s):  
Callorhinus Ursinus ◽  
Naturally Occurring ◽  
Fur Seals ◽  
Northern Fur Seals

Do abiotic mechanisms determine interannual variability in length-at-age of juvenile Arcto-Norwegian cod?

2002 ◽  
Vol 59 (1) ◽  
pp. 57-65 ◽  
Author(s):  
Geir Ottersen ◽  
Kristin Helle ◽  
Bjarte Bogstad
Keyword(s):  
Growth Rates ◽  
Gadus Morhua ◽  
Barents Sea ◽  
Water Masses ◽  
Inverse Relation ◽  
Lower Growth ◽  
Density Dependent ◽  
The Barents Sea ◽  
The Mean ◽  
Dependent Growth

For the large Arcto-Norwegian stock of cod (Gadus morhua L.) in the Barents Sea, year-to-year variability in growth is well documented. Here three hypotheses for the observed inverse relation between abundance and the mean length-at-age of juveniles (ages 1–4) are suggested and evaluated. Based on comprehensive data, we conclude that year-to-year differences in length-at-age are mainly determined by density-independent mechanisms during the pelagic first half year of the fishes' life. Enhanced inflow from the southwest leads to an abundant cohort at the 0-group stage being distributed farther east into colder water masses, causing lower postsettlement growth rates. We can not reject density-dependent growth effects related to variability in food rations, but our data do not suggest this to be the main mechanism. Another hypothesis suggests that lower growth rates during periods of high abundance are a result of density-dependent mechanisms causing the geographic range of juveniles to extend eastwards into colder water masses. This is rejected mainly because year-to-year differences in mean length are established by age 2, which is too early for movements over large distances.

Estimating the Juvenile Survival Rate of Male Northern Fur Seals (Callorhinus ursinus)

1989 ◽  
Vol 46 (8) ◽  
pp. 1428-1436 ◽  
Author(s):  
Andrew W. Trites
Keyword(s):  
Survival Rate ◽  
Juvenile Survival ◽  
Callorhinus Ursinus ◽  
Strongly Correlated ◽  
Fur Seals ◽  
Commercial Harvest ◽  
Northern Fur Seals ◽  
Back Calculation ◽  
Number Of Males ◽  
Insight Into

Three methods for estimating the survival rate of juvenile northern fur seals (Callorhinus ursinus) are developed from the earlier works of Chapman, Smith and Polacheck and Lander. Each of the methods I propose divides the estimated number of males alive at 2 yr of age by the estimated number of pups born in their year class. The number of surviving juveniles are reconstructed by back calculation using the number of males killed during the commercial harvest and the subsequent counts of bulls. The three methods differ in their assumptions concerning subadult survival and escapement from the harvest, although all produce similar estimates when applied to the St. Paul Island fur seals. These new estimates of juvenile survival (1950–80) are strongly correlated with the ratio of cohort kill to pup production and with estimates from the currently-used Lander procedure. This is because the harvest morality of males is large compared with natural morality. The new methods perform acceptably over a wider class of data than Lander's. Their greatest advantage over current procedures is that they provide a better insight into the reliability of the survival estimates they produce.

Digeneans of northern fur seals Callorhinus ursinus (Pinnipedia: Otariidae) from five subpopulations on St. Paul Island, Alaska

2018 ◽  
Vol 117 (4) ◽  
pp. 1079-1086 ◽  
Author(s):  
T. A. Kuzmina ◽  
V. V. Tkach ◽  
T. R. Spraker ◽  
E. T. Lyons ◽  
O. Kudlai
Keyword(s):  
Callorhinus Ursinus ◽  
Fur Seals ◽  
Northern Fur Seals

At-sea behavior of juvenile male northern fur seals (Callorhinus ursinus)

2004 ◽  
Vol 82 (10) ◽  
pp. 1621-1637 ◽  
Author(s):  
J T Sterling ◽  
R R Ream
Keyword(s):  
Body Mass ◽  
Mass Gain ◽  
Callorhinus Ursinus ◽  
Juvenile Male ◽  
Deep Waters ◽  
Fur Seals ◽  
Straight Line ◽  
Northern Fur Seals ◽  
Straight Line Distance ◽  
Pribilof Islands

The at-sea behavior of juvenile male northern fur seals, Callorhinus ursinus (L., 1758), captured at two haul-out sites on St. Paul Island, Alaska, during the 1999 and 2000 breeding seasons (July–September) was studied. To compare at-sea locations, dive behavior, and changes in body mass, 31 juveniles between the estimated ages of 3–6 years were captured, instrumented, and released. Individuals behaved like central-place foragers by making trips to sea and returning to the Pribilof Islands. Trip durations ranged between 8.74 and 29.81 d, whereas distances from departure site ranged between 171.27 and 680.68 km (maximum straight-line distance). Differences in maximum straight-line distance traveled and trip duration were not observed when comparing years or departure site. Diving tended to reflect patterns associated with different bathymetric domains; shallow nighttime diving was common in ~3000 m deep waters, whereas deeper diving was generally observed in <200 m deep waters. Proportion of body mass gained over a single trip to sea averaged 27.8% (range 3%–65%, n = 19). Mass gain was similar between individuals that dove in shallow waters (over the continental shelf; 10.9 ± 1.8 kg (mean ± 1 SE), n = 11) versus individuals that dove in pelagic waters (8.5 ± 1.0 kg, n = 8). These results demonstrate that the at-sea behavior of juvenile males can extend farther from the Pribilof Islands when compared with previous reports of parturient female at-sea behavior, thus revealing important variation within this species.

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