Identifying reproductive events using archival tags: egg‐laying behaviour of the small spotted catshark Scyliorhinus canicula

The use of archival depth telemetry as a means of remotely assessing the reproductive rates of free‐ranging fishes is explored. This is achieved by electronically tracking the vertical movements of individual female small spotted catsharks Scyliorhinus canicula in the natural environment, whilst simultaneously evaluating the temporal and vertical distributions of egg‐laying in this species. Distinctive patterns of short‐term (0·3–3·7 h), shallow‐water activity are documented in the time–depth profiles of female S. canicula that occur at an appropriate depth (1·0–2·3 m) and periodicity (every 10–12 days) to represent egg‐laying behaviour. Putative egg‐laying behaviour was exhibited simultaneously by two individually tracked female S. canicula during late‐spring and early‐summer. The results highlight that, provided species behaviour is suitable and complementary methods such as previous data, laboratory experiments and field surveys can be used to validate the patterns observed, archival depth telemetry offers an unobtrusive means by which egg production and egg‐laying behaviour of free‐living fishes can be estimated. As precise information regarding life‐history parameters is difficult to obtain for free‐ranging fish species, this technique could be used to improve the parameterization of species demographic models that are relevant to the management of wild fish populations.     

Scaling laws of ambush predator ‘waiting’ behaviour are tuned to a common ecology

The decisions animals make about how long to wait between activities can determine the success of diverse behaviours such as foraging, group formation or risk avoidance. Remarkably, for diverse animal species, including humans, spontaneous patterns of waiting times show random ‘burstiness’ that appears scale-invariant across a broad set of scales. However, a general theory linking this phenomenon across the animal kingdom currently lacks an ecological basis. Here, we demonstrate from tracking the activities of 15 sympatric predator species (cephalopods, sharks, skates and teleosts) under natural and controlled conditions that bursty waiting times are an intrinsic spontaneous behaviour well approximated by heavy-tailed (power-law) models over data ranges up to four orders of magnitude. Scaling exponents quantifying ratios of frequent short to rare very long waits are species-specific, being determined by traits such as foraging mode (active versus ambush predation), body size and prey preference. A stochastic–deterministic decision model reproduced the empirical waiting time scaling and species-specific exponents, indicating that apparently complex scaling can emerge from simple decisions. Results indicate temporal power-law scaling is a behavioural ‘rule of thumb’ that is tuned to species’ ecological traits, implying a common pattern may have naturally evolved that optimizes move–wait decisions in less predictable natural environments.     

Regional climatic warming drives long-term community changes of British marine fish

Climatic change has been implicated as the cause of abundance fluctuations in marine fish populations worldwide, but the effects on whole communities are poorly understood. We examined the effects of regional climatic change on two fish assemblages using independent datasets from inshore marine (English Channel, 1913-2002) and estuarine environments (Bristol Channel, 1981-2001). Our results show that climatic change has had dramatic effects on community composition. Each assemblage contained a subset of dominant species whose abundances were strongly linked to annual mean sea-surface temperature. Species' latitudinal ranges were not good predictors of species-level responses, however, and the same species did not show congruent trends between sites. This suggests that within a region, populations of the same species may respond differently to climatic change, possibly owing to additional local environmental determinants, interspecific ecological interactions and dispersal capacity. This will make species-level responses difficult to predict within geographically differentiated communities.     

Sex differences in dogfish behaviour: alternative activity patterns and habitat choice

Guppies are highly sexually dimorphic and females have been shown to mate preferentially with males with various visible traits. Guppies, however, have been shown to respond behaviourally to odour cues from conspecifics. Using a specially designed olfactory choice tank, we tested whether females (1) could detect other guppies on the basis of their olfactory cues alone, (2) preferred to associate with males or with females and (3) could distinguish between different males. Female guppies were found to associate preferentially with other guppies when given a choice between water containing cues from another fish and water containing no cues. When females were presented with olfactory cues from a male or a female, they preferred the female initially but most then reversed their decision and swam to the male. Females associated preferentially with certain males based upon olfactory cues alone. Males, however, preferred on the basis of olfactory cues were the least preferred for visual cues.     

Movement and behaviour patterns of the critically endangered common skate Dipturus batis revealed by electronic tagging

Understanding animal distributions and habitat utilisation is vital for the management of populations, especially those of endangered species. However, this information is not available for the majority of marine species and is difficult to obtain for those with low population densities. The common skate, Dipturus batis, was once abundant and widespread in the North-East Atlantic but is now thought to be locally extinct in the Irish Sea and in the central and southern North Sea, and is listed as Critically Endangered on the IUCN Red List. The constraints of skate body morphology on locomotory mode assume low levels of activity with long periods spent resting on the seabed, therefore predicting a high degree of site fidelity. To investigate this hypothesis we tagged 8 common skate (two male and six female, mass range: 10.9–63.5 kg) with depth and temperature-logging data storage tags off the west coast of Scotland in May 2008. All 6 tags attached to females were recovered after 1–9 months at liberty. All 6 individuals exhibited pronounced site fidelity to highly localised areas. Within these local areas however, time-depth profiles were dominated by periods of high activity, with vertical movements of > 100 m being conducted on a regular, sometimes daily, basis. Intra-individual plasticity was observed in vertical activity patterns with individuals switching between low and high activity patterns. Smaller skate were generally less active and occupied deeper depths. Limited short-term horizontal movements in preferred habitats supporting apparently high foraging activity highlights the need for spatial management of ‘refugial’ populations of this once widespread fish, that appears now largely extirpated from European waters.     

Hunt warm, rest cool: bioenergetic strategy underlying diel vertical migration of a benthic shark

1. Diel vertical migration (DVM) is a widespread phenomenon among marine and freshwater organisms and many studies with various taxa have sought to understand its adaptive significance. Among crustacean zooplankton and juveniles of some fish species DVM is accepted widely as an antipredator behaviour, but little is known about its adaptive value for relatively large-bodied, adult predatory fish such as sharks. Moreover, the majority of studies have focused on pelagic forms, which raises the question of whether DVM occurs in bottom-living predators. 2. To investigate DVM in benthic predatory fish in the marine environment and to determine why it might occur we tracked movements of adult male dogfish (Scyliorhinus canicula) by short- and long-term acoustic and archival telemetry. Movement studies were complemented with measurements of prey abundance and availability and thermal habitat within home ranges. A thermal choice experiment and energy budget modelling was used to investigate trade-offs between foraging and thermal habitat selection. 3. Male dogfish undertook normal DVM (nocturnal ascent) within relatively small home ranges (-100 x 100 m) comprising along-bottom movements up submarine slopes from deeper, colder waters occupied during the day into warmer, shallow prey-rich areas above the thermocline at night. Few daytime vertical movements occurred. Levels of activity were higher during the night above the thermocline compared to below it during the day indicating they foraged in warm water and rested in colder depths. 4. A thermal choice experiment using environmentally realistic temperatures supported the field observation that dogfish positively avoided warmer water even when it was associated with greater food availability. Males in laboratory aquaria moved into warm water from a cooler refuge only to obtain food, and after food consumption they preferred to rest and digest in cooler water. 5. Modelling of energy budgets under different realistic thermal-choice scenarios indicated dogfish adopting a 'hunt warm - rest cool' strategy could lower daily energy costs by just over 4%. Our results provide the first clear evidence that are consistent with the hypothesis that a benthic marine-fish predator utilizes DVM as an energy conservation strategy that increases bioenergetic efficiency.     

Reproductive allocation by the blow fly Lucilia sericata in response to protein limitation

Adult females of the anautogenous blow fly Lucilia sericata (Meigen) (Diptera: Calliphoridae) were fed standardized meals of liquidized liver, in quantities shown to range around the minimum required to initiate yolk deposition. Females from each feeding regime were dissected at daily intervals between 4 and 11 days of age; the number and stage of development of all oöcytes were recorded. Once an initial threshold quantity of protein was ingested, yolk deposition was initiated in all available oöcytes. Subsequently, one of two distinct developmental pathways was followed: arrested development in all oöcytes at an early stage of yolk deposition, or more extensive yolk deposition followed by progressive oösorbtion and the maturation of small batches of eggs. The proportion of females showing oösorbtion relative to arrested follicular development increased with increasing protein meal size, suggesting that the difference in response may be triggered by a second protein threshold, either side of which the arrested development or oösorbtion pathways are followed. The behaviour observed may reflect strategies to maximize reproductive output in this short‐lived, resource‐limited insect species. Flies that display arrested development may have sufficient protein to mature few if any complete eggs, but may subsequently be able to mature a full egg‐batch if they obtain further protein meals; this possibility is offset by the risk of death before finding such a meal. Flies that show oöcyte development and oösorbtion produce smaller egg batches more quickly and hence have a higher probability of achieving at least some reproductive output. By initiating yolk deposition in all oöcytes, female L. sericata retain the potential to adopt either developmental pathway, depending on subsequent protein intake.