Tim D. Smith

Genetic tagging of humpback whales

The ability to recognize individual animals has substantially increased our knowledge of the biology and behaviour of many taxa. However, not all species lend themselves to this approach, either because of insufficient phenotypic variation or because tag attachment is not feasible. The use of genetic markers (‘tags’) represents a viable alternative to traditional methods of individual recognition, as they are permanent and exist in all individuals. We tested the use of genetic markers as the primary means of identifying individuals in a study of humpback whales in the North Atlantic Ocean. Analysis of six microsatellite loci, among 3,060 skin samples collected throughout this ocean allowed the unequivocal identification of individuals. Analysis of 692 ‘recaptures’, identified by their genotype, revealed individual local and migratory movements of up to 10,000 km, limited exchange among summer feeding grounds, and mixing in winter breeding areas, and also allowed the first estimates of animal abundance based solely on genotypic data. Our study demonstrates that genetic tagging is not only feasible, but generates data (for example, on sex) that can be valuable when interpreting the results of tagging experiments.

Segregation of migration by feeding ground origin in North Atlantic humpback whales (Megaptera novaeangliae)

Results from a large-scale, capture–recapture study of humpback whales Megaptera novaeangliae in the North Atlantic show that migration timing is influenced by feeding ground origin. No significant differences were observed in the number of individuals from any feeding area that were re-sighted in the common breeding area in the West Indies. However, there was a relationship between the proportion (logit transformed) of West Indies sightings and longitude (r 2 = 0.97,F1,3 = 98.27,P = 0.0022) suggesting that individuals feeding farther to the east are less likely to winter in the West Indies. A relationship was also detected between sighting date in the West Indies and feeding area. Mean sighting dates in the West Indies for individuals identified in the Gulf of Maine and eastern Canada were significantly earlier than those for animals identified in Greenland, Iceland and Norway (9.97 days, t179 = 3.53, P = 0.00054). There was also evidence for sexual segregation in migration; males were seen earlier on the breeding ground than were females (6.63 days, t105 = 1.98, P = 0.050). This pattern was consistently observed for animals from all feeding areas; a combined model showed a significant effect for both sex (F1 = 5.942, P = 0.017) and feeding area (F3 = 4.756,P = 0.0038). The temporal difference in occupancy of the West Indies between individuals from different feeding areas, coupled with sexual differences in migratory patterns, presents the possibility that there are reduced mating opportunities between individuals from different high latitude areas.

RBM3 mediates structural plasticity and protective effects of cooling in neurodegeneration

In the healthy adult brain synapses are continuously remodelled through a process of elimination and formation known as structural plasticity. Reduction in synapse number is a consistent early feature of neurodegenerative diseases, suggesting deficient compensatory mechanisms. Although much is known about toxic processes leading to synaptic dysfunction and loss in these disorders, how synaptic regeneration is affected is unknown. In hibernating mammals, cooling induces loss of synaptic contacts, which are reformed on rewarming, a form of structural plasticity. We have found that similar changes occur in artificially cooled laboratory rodents. Cooling and hibernation also induce a number of cold-shock proteins in the brain, including the RNA binding protein, RBM3 (ref. 6). The relationship of such proteins to structural plasticity is unknown. Here we show that synapse regeneration is impaired in mouse models of neurodegenerative disease, in association with the failure to induce RBM3. In both prion-infected and 5XFAD (Alzheimer-type) mice, the capacity to regenerate synapses after cooling declined in parallel with the loss of induction of RBM3. Enhanced expression of RBM3 in the hippocampus prevented this deficit and restored the capacity for synapse reassembly after cooling. RBM3 overexpression, achieved either by boosting endogenous levels through hypothermia before the loss of the RBM3 response or by lentiviral delivery, resulted in sustained synaptic protection in 5XFAD mice and throughout the course of prion disease, preventing behavioural deficits and neuronal loss and significantly prolonging survival. In contrast, knockdown of RBM3 exacerbated synapse loss in both models and accelerated disease and prevented the neuroprotective effects of cooling. Thus, deficient synapse regeneration, mediated at least in part by failure of the RBM3 stress response, contributes to synapse loss throughout the course of neurodegenerative disease. The data support enhancing cold-shock pathways as potential protective therapies in neurodegenerative disorders.

ASSESSING THE EFFECTIVENESS OF RELEASING COD LARVAE FOR STOCK IMPROVEMENT WITH MONITORING DATA

Beginning in the 1880s, management of marine fisheries by hatching and releasing yolk-sac-stage larvae was advocated in both the United States and Norway. Major cod hatchery programs were popular in both countries until the mid-20th century, despite lack of evidence that cod abundance increases with release of hatchery-reared fish larvae; the potential value for such management procedures was repeatedly advocated throughout the 20th century. In Norway, a beach-seine monitoring program was begun in the early 1900s to collect data on fall abundance of 6-mo-old demersal fish in 21 fjords along the Norwegian Skagerrak coast and is still going on. We used these data in conjunction with hatchery data on numbers of yolk-sac larval cod released each spring in several fjords to test for an effect of the releases on the abundance of fjord cod populations. Using both a permutation test and a statistically derived time-series model for the cods population dynamics, we found a slight, but statistically significant, dependence of 6-mo-old cod abundance on the number of yolk-sac larvae released in four of the 16 fjords (for which we had adequate release and beach-seine data needed for carrying out the testing). However, using the time-series model, we did not find evidence of long-term increases in the abundance of mature cod in any of the fjords. We discuss our findings on the basis of the literature on marine fish population enhancement programs worldwide.

Interactions between marine mammals and fisheries: an unresolved problem for fisheries research

Abstract Food web interactions between marine mammals and commercial fisheries have been subject to relatively little attention in fishery research. Three characteristics of marine mammals, commercial fisheries, and the conduct of fisheries research have contributed to this. These include differences between marine mammals and fishermen in prey size capability and ability to adapt to rapid changes, major undocumented ecological changes which have occurred historically making it difficult to interpret present ecosystem states, and a short term focus which was adopted by fishery research during its development towards the direct effects of harvesting. These characteristics need to be considered in designing and implementing research programs to investigate interactions between marine mammals and fisheries.