Eight-year study of social and ecological correlates of mortality among immature baboons of Mikumi National Park,Tanzania

The Cox Proportional Hazards Regression Model was used to examine ecological and sociodemographic correlates of mortality among 164 immature yellow baboons born over an 8-year period at Mikumi National Park, Tanzania. Ecological correlates were derived from seasonal rainfall. Mortality was lowest for immatures born during the late rainy season, when it was likely that nourishment for pregnant and lactating females was greatest. High mortality was associated with above-average rainfall early in the immature's first complete rainy season. This association may result from one or more of the following: exposure, increased ranging, or accelerated vegetation growth, each of which is thought to increase hazards for weanlings. When births for the 8 years of the study were pooled, a birth peak occurred during the early dry season. The larger number of births during a birth peak should intensify competition among mothers and among immatures. Mortality was greatest for immature females born during the season immediately following the birth peak, while lowest for immature females born during the season immediately preceding the peak. Immature female mortality was greatest when the troop size at birth was large, and was most severe for females born to low ranking mothers. The sociodemographic results are consistent with Wasser's hypothesis that cooperative attacks of female baboons upon other troop females suppress the others' reproduction and the vitality of their infants, thereby improving the relative competitive position of the attackers' own young.     

Characterization of twenty‐four microsatellite markers for rainbow trout (Oncorhynchus mykiss)

Twenty‐four new microsatellite markers were developed for genome mapping and population genetics studies in rainbow trout (Oncorhynchus mykiss). The amount of polymorphism, percentage heterozygosity and ability of each marker to amplify genomic DNA from other salmonids were recorded. Seven markers were observed to be duplicated in the rainbow trout genome by containing more than one allele in homozygous (clonal) fish.     

Stress from air emersion fails to alter chloride cell numbers in the gills of rainbow trout

Air emersion stress caused an elevation in blood plasma cortisol of rainbow trout Oncorhynchus mykiss but this acute stressor did not elicit chloride cell proliferation in the gill tissue within 2 weeks following the disturbance.     

Temperature dependence of predation depends on the relative performance of predators and prey

The temperature dependence of predation rates is a key issue for understanding and predicting the responses of ecosystems to climate change. Using a simple mechanistic model, we demonstrate that differences in the relative performances of predator and prey can cause strong threshold effects in the temperature dependence of attack rates. Empirical data on the attack rate of northern pike (Esox lucius) feeding on brown trout (Salmo trutta) confirm this result. Attack rates fell sharply below a threshold temperature of +11°C, which corresponded to a shift in relative performance of pike and brown trout with respect to maximum attack and escape swimming speeds. The average attack speed of pike was an order of magnitude lower than the escape speed of brown trout at 5°C, but approximately equal at temperatures above 11°C. Thresholds in the temperature dependence of ecological rates can create tipping points in the responses of ecosystems to increasing temperatures. Thus, identifying thresholds is crucial when predicting future effects of climate warming.     

Direct estimates of the selectivity of a multimesh and a series of single gillnets for brown trout

Hatchery brown trout Salmo trutta (1406) of length 5–20 cm were released into a 7.5 ha shallow lake. They were recaptured with 28 multimesh gillnets of a type proposed for use in the Nordic countries and 42 single gillnets of mesh size 8–22 mm (knot to knot). Corrected for the effect of different twine thicknesses, the single nets showed the highest selectivity for 16.5 mm and smaller meshes and the multimesh nets for the larger meshes. The height of the selectivity curves increased exponentially with mesh size, and most distinctly for the multimesh nets. Over a limited range of mesh sizes the selectivity of the two types of net did not differ much. Extended over mesh sizes 10.0–55.0 mm, the catching abilities of the two types of net became considerably different.     

Cadmium exposure of rainbow trout, Salmo gairdneri Richardson: effects on immune functions

Differential leucocyte counts, phagocytosis, humoral antibody response and the in vitro blasto-genetic response to mitogens (lipopolysaccharide and Concanavalin A) and to an antigen ( Vibrio anguillarum ) were studied in rainbow trout exposed to 0,0.7 or 3.6 μg Cd 1⁻¹ for 12 weeks.
Although the fish did not exhibit any clinical or histological changes, cadmium exposure was found to affect two of the immune parameters measured. The cellular response of fish immunized with V. anguillarum to the homologous antigen was significantly lower for splenocytes obtained from fish exposed to cadmium for 9 weeks (3.6 μg Cd 1⁻¹ group) than for splenocytes obtained from non-exposed fish. Conversely, the humoral antibody response to V. anguillarum O-antigen was higher in the 3.6 μg Cd 1⁻¹ group than in the non-exposed group. Protective immunity of fish vaccinated against V. anguillarum was equally as good in the cadmium-exposed group as in the non-exposed group. No cadmium-induced changes in differential leucocyte counts or in the proportions of phagocytic cells were observed.     

Anadromous trout threatened by whitefish gill‐net fisheries in the northern Baltic Sea

We estimated the effect of the gill‐net fisheries targeted at whitefish (Coregonus sp.) on anadromous sea trout, Salmo trutta, in the Gulf of Bothnia, Baltic Sea using separate data for fish species. The analysis of sea trout captures was based on tagging and recapture data collected in 1998–2011, while whitefish data were derived from individual samples of commercial fisheries from the same period. The mesh sizes used in gill‐net fishing and the seasonal and temporal distributions of recaptured sea trout and sampled whitefish were compared in the northern and southern Gulf of Bothnia. The trout had typically spent 1–2 years at sea, and they were mainly immature with a median body length of 40–43 cm at the time of recapture in gill nets. Despite the increase in the minimum permitted landing size from 40 to 50 cm in 2008, the median length of recaptured trout remained unchanged during the study period. Most (59%) of the gillnetted trout were caught in the southern Gulf of Bothnia in gill nets with mesh sizes of 40–45 mm, which were also used in the whitefish fishery (72%). In the northern Gulf of Bothnia, nets with a smaller mesh size of 25–39 mm took 83% of the whitefish catch and 39% from recaptured trout. In both areas, the overlap in mesh sizes used to gill‐net catch whitefish and sea trout increased during the study period. There were clear seasonal and areal differences in the relative probability of sea trout being captured in gill nets, suggesting that carefully tailored spatial and temporal restrictions on gill‐net fisheries could provide a tool to protect young sea trout without causing intolerable difficulties for the fisheries targeting other species.     

Alaskan brown bears (Ursus arctos) aggregate and display fidelity to foraging neighborhoods while preying on Pacific salmon along small streams

The interaction between brown bears (Ursus arctos) and Pacific salmon (Oncorhynchus spp.) is important to the population dynamics of both species and a celebrated example of consumer‐mediated nutrient transport. Yet, much of the site‐specific information we have about the bears in this relationship comes from observations at a few highly visible but unrepresentative locations and a small number of radio‐telemetry studies. Consequently, our understanding of brown bear abundance and behavior at more cryptic locations where they commonly feed on salmon, including small spawning streams, remains limited. We employed a noninvasive genetic approach (barbed wire hair snares) over four summers (2012–2015) to document patterns of brown bear abundance and movement among six spawning streams for sockeye salmon, O. nerka, in southwestern Alaska. The streams were grouped into two trios on opposite sides of Lake Aleknagik. Thus, we predicted that most bears would forage within only one trio during the spawning season because of the energetic costs associated with swimming between them or traveling around the lake and show fidelity to particular trios across years because of the benefits of familiarity with local salmon dynamics and stream characteristics. Huggins closed‐capture models based on encounter histories from genotyped hair samples revealed that as many as 41 individuals visited single streams during the annual 6‐week sampling season. Bears also moved freely among trios of streams but rarely moved between these putative foraging neighborhoods, either during or between years. By implication, even small salmon spawning streams can serve as important resources for brown bears, and consistent use of stream neighborhoods by certain bears may play an important role in spatially structuring coastal bear populations. Our findings also underscore the efficacy of noninvasive hair snagging and genetic analysis for examining bear abundance and movements at relatively fine spatial and temporal scales.     

Genetic differentiation of populations of the copepod sea louse Lepeophtheirus salmonis (Krøyer) ectoparasitic on wild and farmed salmonids around the coasts of Scotland: Evidence from RAPD markers

Sea trout are the sea-going migratory form of the freshwater brown trout (Salmo trutta L.) and since 1989 there have been marked declines in their stocks on the west coasts both of Scotland and Ireland. Various factors have been attributed as possible causal agents in these stock declines, including fresh water acidification, overfishing, climatic fluctuations, habitat degradation and sea lice parasitic burdens. The putative impact of infestations of sea trout by the ectoparasitic copepod sea louse, Lepeophtheirus salmonis (Krøyer), has featured prominently in the controversy, especially with regard to the role of inshore commercial salmon farms as a possible source of infestation of wild salmonids by sea lice. This study focused on the population genetics of L. salmonis around the coasts of Scotland: We sampled fish from wild and cultured stocks and included salmon (Salmo salar L.), rainbow trout (Oncorhynchus mykiss Walbaum) and sea trout as host species. Analyses of allozyme variation of sea lice were confined to data for two polymorphic loci (Fum, Got-2) and conformed to our initial expectation — that the inclusion of a planktonic larval phase in the life cycle of the copepod, in addition to the high mobility of the host fish, would enhance gene flow and preclude genetic differentiation of L. salmonis populations as a result of random drift alone. DNA polymorphism was quantified by means of PCR and RAPD analysis. Six primers were screened for 16 samples (from wild and farmed salmon, wild sea trout and farmed rainbow trout) — including the east, north and west coasts of Scotland — and the data analyzed by AMOVA (Analysis of Molecular Variance). In contrast to the allozyme results, the RAPD analysis showed striking patterns of genetic differentiation around the coasts of Scotland. The overall pattern was one of genetic homogeneity of L. salmonis populations sampled from wild salmon and sea trout. All of the L. salmonis samples taken from farmed salmon and rainbow trout did, however, show highly significant levels of genetic differentiation, both between wild and farmed salmonids and among the various farms themselves. Evidence of high levels of small-scale spatial or temporal heterogeneity of RAPD marker band frequencies was shown for the one farm from which repeat samples (July and November, 1995) were analysed. Samples of sea lice taken from west coast wild sea trout subjected to RAPD analysis also revealed the occurrence of putative “farm markers” in some individual parasites, indicating that they had possibly originated from salmon farms.     

Discrimination of native and introduced brown trout in the River Doubs (Rhône drainage) by number and shape of parr marks

Significant differences in the number and shape of parr marks were found between native, introduced hatchery and hybrid brown trout parr in the River Doubs. Similar differences in number of parr marks were observed in selective cross-breedings.