Multiscale relationships between humpback whales and forage species hotspots within a large marine ecosystem.

Fluctuations in prey abundance, composition, and distribution can impact predators, and when predators and fisheries target the same species, predators become essential to ecosystem-based management. Because of the difficulty in collecting concomitant predator-prey data at appropriate scales in patchy environments, few studies have identified strong linkages between cetaceans and prey, especially across large geographic areas. During summer 2018, a line-transect survey for cetaceans and coastal pelagic species was conducted over the continental shelf and slope of British Columbia, Canada, and the US West Coast, allowing for a large-scale investigation of predator-prey spatial relationships.

Length conversions and mass-length relationships of five forage-fish species in the California current ecosystem.

Length-measurement conversions and seasonal mass-length relationships (MLR) for Pacific herring Clupea pallasii, northern anchovy Engraulis mordax, Pacific sardine Sardinops sagax, Pacific mackerel Scomber japonicus and jack mackerel Trachurus symmetricus in the California Current are presented. The conversions between total (L ), fork (L ,) and standard lengths (L ) should facilitate comparisons of data across disciplines and institutions. These equations resulted from an analysis of measurements spanning 14 years and the western seaboard of North America, from the north end of Vancouver Island to the USA-Mexico border.

Estimating fish abundance at spawning aggregations from courtship sound levels.

Sound produced by fish spawning aggregations (FSAs) permits the use of passive acoustic methods to identify the timing and location of spawning. However, difficulties in relating sound levels to abundance have impeded the use of passive acoustics to conduct quantitative assessments of biomass. Here we show that models of measured fish sound production versus independently measured fish density can be generated to estimate abundance and biomass from sound levels at FSAs.

Comparisons among ten models of acoustic backscattering used in aquatic ecosystem research.

Analytical and numerical scattering models with accompanying digital representations are used increasingly to predict acoustic backscatter by fish and zooplankton in research and ecosystem monitoring applications. Ten such models were applied to targets with simple geometric shapes and parameterized (e.g.

A cold oceanographic regime with high exploitation rates in the Northeast Pacific forecasts a collapse of the sardine stock.

The oceanographic conditions in the north Pacific have shifted to a colder period, Pacific sardine (Sardinops sagax) biomass has declined precipitously in the California Current, the international sardine fishery is collapsing, and mackerel (Trachurus symmetricus and Scomber japonicus) are thriving. This situation occurred in the mid-1900s, but indices of current oceanographic conditions and the results of our acoustic-trawl surveys indicate it likely is recurring now, perhaps with similar socioeconomic and ecological consequences. Also alarming is the repetition of the fishery's response to a declining sardine stock-progressively higher exploitation rates targeting the oldest, largest, and most fecund fish.

Absolute measurements of total target strength from reverberation in a cavity.

A new method was developed to acoustically measure the density and total scattering cross-section (sigma(t)) or total target strength [TTS = 10log10(sigma(t)/4pi)] of objects in motion in a highly reflective cavity [J. De Rosny and P. Roux, J.