Food consumption estimates of Barents Sea harp seals

Interaction between three key species in the sea ice-reduced Arctic Barents Sea system

Population dynamics depend on trophic interactions that are affected by climate change. The rise in sea temperature is associated with the disappearance of sea ice in the Arctic. In the Arctic part of the Barents Sea, Atlantic cod, capelin and polar cod are three fish populations that interact and are confronted with climate-induced sea ice reductions. The first is a major predator in the system, while the last two are key species in Arctic and sub-Arctic ecosystems, respectively. There are still many unknowns regarding how predicted environmental change may influence the joint dynamics of these populations. Using time series from a 32 year long survey, we developed a state-space model that jointly modelled the dynamics of cod, capelin and polar cod. Using a hindcast scenario approach, we projected the effect of reduced sea ice on these populations. We show that the impact of sea ice reduction and concomitant sea temperature increase may lead to a decrease of polar cod abundance at the benefit of capelin but not of cod which may decrease, resulting in strong changes in the food web. Our analyses show that climate change in the Arcto-boreal system can generate different species assemblages and new trophic interactions, which is the knowledge needed for effective management measures.

A review of bioenergetic modelling for marine mammal populations

Bioenergetic models describe the processes through which animals acquire energy from resources in the environment and allocate it to different life history functions. They capture some of the fundamental mechanisms regulating individuals, populations and ecosystems and have thus been used in a wide variety of theoretical and applied contexts. Here, I review the development of bioenergetic models for marine mammals and their application to management and conservation. For these long-lived, wide-ranging species, bioenergetic approaches were initially used to assess the energy requirements and prey consumption of individuals and populations. Increasingly, models are developed to describe the dynamics of energy intake and allocation and predict how resulting body reserves, vital rates and population dynamics might change as external conditions vary. The building blocks required to develop such models include estimates of intake rate, maintenance costs, growth patterns, energy storage and the dynamics of gestation and lactation, as well as rules for prioritizing allocation. I describe how these components have been parameterized for marine mammals and highlight critical research gaps. Large variation exists among available analytical approaches, reflecting the large range of life histories, management needs and data availability across studies. Flexibility in modelling strategy has supported tailored applications to specific case studies but has resulted in limited generality. Despite the many empirical and theoretical uncertainties that remain, bioenergetic models can be used to predict individual and population responses to environmental change and other anthropogenic impacts, thus providing powerful tools to inform effective management and conservation.

Temporal dynamics of top predators interactions in the Barents Sea

The Barents Sea system is often depicted as a simple food web in terms of number of dominant feeding links. The most conspicuous feeding link is between the Northeast Arctic cod Gadus morhua, the world's largest cod stock which is presently at a historical high level, and capelin Mallotus villosus. The system also holds diverse seabird and marine mammal communities. Previous diet studies may suggest that these top predators (cod, bird and sea mammals) compete for food particularly with respect to pelagic fish such as capelin and juvenile herring (Clupea harengus), and krill. In this paper we explored the diet of some Barents Sea top predators (cod, Black-legged kittiwake Rissa tridactyla, Common guillemot Uria aalge, and Minke whale Balaenoptera acutorostrata). We developed a GAM modelling approach to analyse the temporal variation diet composition within and between predators, to explore intra- and inter-specific interactions. The GAM models demonstrated that the seabird diet is temperature dependent while the diet of Minke whale and cod is prey dependent; Minke whale and cod diets depend on the abundance of herring and capelin, respectively. There was significant diet overlap between cod and Minke whale, and between kittiwake and guillemot. In general, the diet overlap between predators increased with changes in herring and krill abundances. The diet overlap models developed in this study may help to identify inter-specific interactions and their dynamics that potentially affect the stocks targeted by fisheries.

Development enhances hypometabolism in northern elephant seal pups (Mirounga angustirostris)

Investigation into the development of oxygen storage capacity in air-breathing marine predators has been performed, but little is known about the development of regulatory factors that influence oxygen utilization. Strategies for efficiently using oxygen stores should enable marine predators to optimize time spent foraging underwater.We describe the developmental patterns of oxygen use during voluntary breath-holds in northern elephant seals (Mirounga angustirostris) at 2 and 7 weeks post-weaning. We measured 1) changes in oxygen consumption (VO₂), and 2) changes in venous pH, partial pressure of oxygen (pO₂), haemoglobin saturation (sO₂), oxygen content (O₂ct), partial pressure of carbon dioxide (pCO₂), haematocrit (Hct) and total haemoglobin (tHb). To examine the effect of the dive response on the development of oxygen utilization, voluntary breath-hold experiments were conducted in and out of water.Suppression of VO₂ during voluntary breath-holds increased significantly between 2 and 7 weeks post-weaning, reaching a maximum suppression of 53% below resting metabolic rate and 56% below Kleiber's standard metabolic rate. From 2 to 7 weeks post-weaning, breath-hold VO₂ was reduced by 52%. Between the two age classes, this equates to a mean breath-hold VO₂ reduction of 16% from resting VO₂. Breath-hold VO₂ also declined with increasing breath-hold duration, but there was no direct effect of voluntary submergence on reducing VO₂.Age did not influence rates of venous pO₂ depletion during breath-holds. However, voluntary submergence did result in slower pO₂ depletion rates when compared to voluntary terrestrial apnoeas. The differences in whole body VO₂ during breath-holds (measured at recovery) and venous pO₂ (reflective of tissue O₂-use measured during breath-holds), likely reflects metabolic suppression in hypoxic, vasoconstricted tissues.Consistent pCO₂ values at the end of all voluntary breath-holds (59.0 ± 0.7 mmHg) suggests the physiological cue for stimulating respiration in northern elephant seal pups is the accumulation of CO₂.Oxygen storage capacity and metabolic suppression directly limit diving capabilities and may influence foraging success in low-weaning weight seals forced to depart to sea prior to achieving full developmental diving capacity.

Reference values for serum biochemical parameters in free-ranging harp seals

BACKGROUND

The harp seal (Phoca groenlandica) is one of the most important predators in the Northeastern Atlantic ecosystem. Establishing biochemical reference intervals is important for evaluating the health status of harp seals kept in captivity and for evaluating the effects of environmental changes on the health of populations in the wild.

OBJECTIVE

The purpose of this study was to determine reference values for serum biochemical parameters in wild adult harp seals using readily available current methods.

METHODS

Blood samples were obtained from 14 adult female harp seals and 9 suckling pups on the pack ice of the Greenland Sea in early March 1998. Seven seals were humanely killed on the ice by permission of the Norwegian Directory of Fisheries and in conjunction with several other research projects. The seals were sampled within 15 minutes postmortem. Remaining seals were captured alive and sampled via the extradural intravertebral vein. Serum biochemical parameters were measured using a Technicon Axon analyzer and included electrolytes (sodium, chloride, potassium, magnesium, and calcium), substrates (free fatty acids, triglycerides, fructosamine, and glucose), end products (urea and uric acid), and proteins (total protein, globulins, and albumin). Serum protein electrophoresis also was done. Data were tested for normality and reference limits were calculated as mean +/- 1.96 X SD. Results between groups were compared using 2-tailed t-tests.

RESULTS

Serum levels of glucose and triglycerides were lower, but serum levels of urea were higher in dead animals than in animals that were captured alive. Serum levels for 7 of 17 parameters were significantly different in pups compared with adults. Separate reference intervals were calculated for adult seals and seal pups.

CONCLUSION

Both sampling method and age should be considered when evaluating the results of future analysis of serum parameters in wild and captive harp seals.