No abstract

Southern flounder ( Paralichthys lethostigma ) exhibit environmental sex determination (ESD), where environmental factors can influence phenotypic sex during early juvenile development but only in the presumed XX female genotype. Warm and cold temperatures masculinize fish with mid-range conditions producing at most 50% females. Due to sexually dimorphic growth, southern flounder fisheries are dependent upon larger females. Wild populations could be at risk of masculinization from ESD due to globally increasing water temperatures. We evaluated the effects of habitat and temperature on wild populations of juvenile southern flounder in North Carolina, USA. While northern habitats averaged temperatures near 23 °C and produced the greatest proportion of females, more southerly habitats exhibited warmer temperatures (>27 °C) and consistently produced male-biased sex ratios (up to 94% male). Rearing flounder in the laboratory under temperature regimes mimicking those of natural habitats recapitulated sex ratio differences observed across the wild populations, providing strong evidence that temperature is a key factor influencing sex ratios in nursery habitats. These studies provide evidence of habitat conditions interacting with ESD to affect a key demographic parameter in an economically important fishery. The temperature ranges that yield male-biased sex ratios are within the scope of predicted increases in ocean temperature under climate change.

Climate change is resulting in decreased sea ice extent and increased industrial activity in Arctic regions. In northern Alaska, USA, sea ice loss has increased the frequency of land-based polar bear Ursus maritimus maternal dens, leading to greater potential for overlap between industrial activities and denning bears. Responses of denning bears to human disturbance could result in costly reproductive outcomes, although observation of these responses is logistically challenging and expensive. We developed a method to standardize the process of classifying the response of denning polar bears to disturbance using decision rules based on polar bear biology and denning chronology. We applied this method to 46 maternal polar bear dens exposed to human activity (e.g. vehicle traffic, ground-based monitoring). Because the timing of disturbance influences the response and subsequent fitness consequences, we determined outcomes specific to 4 denning periods: (1) den establishment (excavation to cub birth); (2) early denning (cub birth to 60 d old); (3) late denning (60 d old to emergence); and (4) post-emergence (emergence to den site departure). We classified the outcomes of 79 exposures as 37 having ‘no documented effect’ (no observed response), 7 as ‘behavioral’ (observed behavioral disruption), 17 as ‘early emergence’ (den emergence occurring earlier than an undisturbed emergence), 14 as ‘early departure’ (den site abandonment post-emergence earlier than if undisturbed), and 4 as ‘cub mortality’ (death or abandonment of ≥1 cub). Outcomes with potential fitness consequences occurred in every denning period. Our classification method facilitated a standardized approach that can be used to classify the outcome of den disturbance. Determining outcomes in relation to a specific denning period may facilitate improved implementation of mitigation strategies to reduce disturbance to denning bears.