Harbor seal pup dispersal and individual morphology, hematology, and contaminant factors affecting survival

This work was funded by The Valentine Family Foundation and the John H. Prescott Marine Mammal Rescue Assistance Grant Program.Understanding the factors affecting individual harbor seal (Phoca vitulina) survival is essential for determining population level health risks. We estimated postweaning dispersal, and modeled the effects of morphology, hematology, and blubber contaminants on the survival of recently weaned harbor seal pups using a mark recapture framework. We deployed satellite transmitters on apparently healthy pups captured in San Francisco Bay (SFB, n = 19) and Tomales Bay (TB, n = 7), and pups released after rehabilitation that stranded along the central California coast preweaning (n = 21). Dispersal distances were further than previously reported for harbor seal pups (maximum = 802 km) which has implications for understanding risks to this vulnerable age class. We found differences in body condition, serum immunoglobulin and thyroxine (T4) concentrations, white blood cell count, and blubber organohalogen contamination (OH) among the three groups. Overall, increased T4, decreased OH, and increased mass were associated with greater survival probabilities; whereas, among stranded seals, greater mass gain, shorter time in rehabilitation, and admission to rehabilitation earlier in the season were associated with greater survival probabilities. Attention to these latter factors may improve the success of rehabilitation efforts. For wild pups, reduction of legacy contaminants and direct causes of mortality, such as ship strike, may enhance pup survival.Publisher PDFPeer reviewe

Postcard Featuring Abraham Lincoln\u27s Face at Mount Rushmore

This postcard features Abraham Lincoln\u27s image at Mt. Rushmore in South Dakota.https://scholarsjunction.msstate.edu/fvw-postcards/2363/thumbnail.jp

Spatial Distribution and Temporal Patterns of Cassin’s Auklet Foraging and Their Euphausiid Prey in a Variable Ocean Environment

<div><p>Krill (<i>Euphausiids)</i> play a vital ecosystem role in many of the world’s most productive marine regions, providing an important trophic linkage. We introduce a robust modeling approach to link Cassin’s auklet (<i>Ptychoramphus aleuticus</i>) abundance and distribution to large-scale and local oceanic and atmospheric conditions and relate these patterns to similarly modeled distributions of an important prey resource, krill. We carried out at-sea strip transect bird surveys and hydroacoustic assessments of euphausiids (2004–2013). Data informed separate, spatially-explicit predictive models of Cassin’s auklet abundance (zero-inflated negative binomial regression) and krill biomass (two-part model) based on these surveys. We established the type of prey responsible for acoustic backscatter by conducting net tows of the upper 50 m during surveys. We determined the types of prey fed to Cassin’s auklet chicks by collecting diet samples from provisioning adults. Using time-depth-recorders, we found Cassin’s auklets utilized consistent areas in the upper water column, less than 30 m, where krill could be found (99.5% of dives were less than 30 m). Birds primarily preyed upon two species of euphausiids, <i>Euphausia pacifica</i> and <i>Thysanoessa spinifera</i>, which were available in the upper water column. Cassin’s auklet abundance was best predicted by both large scale and localized oceanic processes (upwelling) while krill biomass was best predicted by local factors (temperature, salinity, and fluorescence) and both large scale and localized oceanic processes (upwelling). Models predicted varying krill and bird distribution by month and year. Our work informs the use of Cassin’s auklet as a valuable indicator or krill abundance and distribution and strengthens our understanding of the link between Cassin’s auklet and its primary prey. We expect future increases in frequency and magnitude of anomalous ocean conditions will result in decreased availability of krill leading to declines in the Farallon Islands population of Cassin’s auklets.</p></div

Description and ranges of variables used to model krill distribution and Cassin’s auklet abundance using 3 km bins (<i>n</i> = 4313).

<p>All variables were used in both modeling exercises with exception of effort (* used only in krill analysis) or detection (** used only in CAAU analysis) variables.</p><p>⁺ 98% of data observed in a 0 to 2 condition;</p><p>⁺⁺ 99% of data observed in a 0 to 1 m condition.</p><p>Description and ranges of variables used to model krill distribution and Cassin’s auklet abundance using 3 km bins (<i>n</i> = 4313).</p

Predicted krill biomass (g m^-2), 2004–2013 (a-j, sequentially): variations in annual modeled habitat use (predictions averaged over <i>n</i> = 3 months except 2010, <i>n</i> = 4, and 2013, <i>n</i> = 2); each gradation represents a decile, annual mean values with all months pooled per year.

<p>The 200 m isobath and boundaries of National Marine Sanctuaries included in blue and black, respectively.</p

Predicted Cassin’s auklet abundance (birds km^-2) by year, 2004–2013 (a-j, sequentially): variations in annual modeled habitat use; each gradation represents a decile, annual mean values with all months pooled per year.

<p>The 200 m isobath and boundaries of National Marine Sanctuaries included in blue and black, respectively.</p

Predicted (a) krill biomass (g m^-2) and (b) Cassin’s auklet abundance (birds km^-2), 2004–2013: top habitat use model applied across all months and years; each gradation represents a decile.

<p>The 200 m isobath and boundaries of National Marine Sanctuaries included in blue and black, respectively.</p