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Uncrewed surface vehicles (USVs) equipped with echosounders have the potential to replace or enhance acoustic observations from conventional research vessels (RVs), increase spatial and temporal coverage, and reduce cost and carbon emission. We discuss the objectives, system requirements, infrastructure, and regulations for using USVs with echosounders to conduct ecological experiments, acoustic-trawl surveys, and long-term monitoring. We present four example applications of USVs with lengths <8 m, and highlight some advantages and disadvantages relative to RV-based data acquisitions. Sail-driven USVs operate continuously for months and are more mature than motorized USVs, but they are slower. To maintain the pace of an RV, multiple sail-powered USVs sample in coordination. In comparison, motorized USVs can travel as fast as RVs and therefore may facilitate a combined survey, interleaving USV and RV transects, with RV-based biological sampling. Important considerations for all USVs include platform design, noise and transducer motion mitigation, communications and operations infrastructure, onboard data processing, biological sampling approach, and legal requirements. This technology is evolving and applied in multiple disciplines, but further development and institutional commitment are needed to allow USVs equipped with echosounders to become ubiquitous and useful components of a worldwide network of autonomous ocean observation platforms. [ABSTRACT FROM AUTHOR]

Three years after the 2015 collapse of the northern stock of Pacific Sardine that is predominantly located off the west coast of the United States, acoustic‐trawl (A‐T) surveys documented an increase in the presence and persistence of the southern stock off coastal Southern California. Then in 2020, the biomass of Sardine that was landed in Mexico and attributed to the northern stock exceeded the estimated biomass for the entire northern stock. To investigate if the landings were incorrectly classified, we revisit a model of northern‐stock potential habitat and the associated range of sea‐surface temperature (SST) used to apportion the A‐T survey data and monthly fishery landings to the two stocks, respectively. We update the probabilistic model of potential habitat with data on sardine‐egg presence and absence and concomitant satellite‐sensed SST and chlorophyll‐a concentration through 2019 and apply the new model to more accurately attribute the A‐T observations and fishery landings data to the northern or southern stock. The addition of recent data, with increased coverage in SSTs between 15°C and 17°C, improves the model accuracy and spatial precision of the stock attribution. The attribution accuracy is critically dependent on the temporal and spatial coincidence of the environmental and survey or landings data and should be corroborated with other characteristics indicative of biological isolation such as spatial separation, distinct spawning areas and seasons, and uncorrelated demographics. [ABSTRACT FROM AUTHOR]

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. We report on a case study of humpback whales (Megaptera novaeangliae) and their primary prey—Pacific herring (Clupea pallasii), northern anchovy (Engraulis mordax), and krill—using generalized additive models to explore the relationships between whale abundance on 10‐km transect segments and prey metrics. Prey metrics included direct measures of biomass densities on segments and an original hotspot metric. For each prey species, segments in the upper fifth percentile for biomass density (across all segments) were designated hotspots, and whale counts on a segment were evaluated for their relationship to number of hotspot segments (species‐specific and multispecies) within 25, 50, or 100 km. Whale abundance was not strongly related to direct measures of biomass densities, whereas models using hotspot metrics were more effective at describing variation in whale abundance, underscoring that evaluating prey at relevant and measurable scales is critical in patchy, dynamic marine environments. Our analysis highlighted differences in the distribution and prey availability for three humpback whale distinct population segments (DPSs) as defined under the US Endangered Species Act, including threatened and endangered DPSs that forage within the California Current Large Marine Ecosystem. These linkages provide insights into which prey species whales may be targeting in different regions and across multiple scales and, consequently, how climatic variability and anthropogenic risks may differentially impact these distinct predator–prey assemblages. By identifying scale‐appropriate prey hotspots that co‐occur with humpback whale aggregations, and with targeted, consistent prey sampling and estimations of potential consumption rates by whales, these findings can help inform the conservation and management of humpback whales within an ecosystem‐based management framework. [ABSTRACT FROM AUTHOR]

Abstract--The abundances and distributions of coastal pelagic fish species in the California Current Ecosystem from San Diego to southern Vancouver Island, were estimated from combined acoustic and trawl surveys conducted [...]

Abstract--During the last century, the population of Pacific sardine (Sardinops sagax) in the California Current Ecosystem has exhibited large fluctuations in abundance and migration behavior. From approximately 1900 to 1940, [...]

Abundance and distribution of Antarctic krill (Euphausia superba) in the nearshore waters north of Livingston Island, Antarctica, were characterized from six small-boat surveys conducted in late January or early February from 2000 to 2007. The first three surveys (2000, 2002, 2004) were conducted using a 120 kHz split-beam echosounder to measure water column acoustic backscatter. The last three surveys (2005-2007) were conducted using 38 kHz and 200 kHz singlebeam echosounders. A portion of the acoustic backscatter was attributed to Antarctic krill based on the results of net tows, underwater video observations, and a multiple-frequency acoustic classification algorithm. The annual mean krill biomass density in the survey area ranged from 11 to 84 g*[m.sup.-2]. Results are compared with the western Scotia Sea area of the US Antarctic Marine Living Resources (AMLR) program's acoustic surveys of krill biomass density for the same years. Nearshore krill biomass densities were significantly larger (t test, p < 0.05), more stable, and the coefficients of variation were smaller than the much larger AMLR surveys. Increased competition between seals, penguins, and humans for the nearshore krill resource, especially during the austral summer months, could impact the recruitment success of these land-based krill predators. Implications of nearshore krill biomass on small-scale management units are discussed. Resume: Six inventaires en petit navire realisesa la fin de janvier ou au de but de fevrier de 2000 a 2007 nous ont servia caracte riser labondance et la repartition du krill antarctique (Euphausia superba) dans les eaux cotieres au nord de l'ile Livingston, Antarctique. Les trois premiers inventaires (2000, 2002, 2004) ont ete faits a laide d'un echosondeur de 120 kHz a faisceau divise afin de mesurer la retrodiffusion acoustique dans la colonne d'eau. Les trois derniers inventaires (2005-2007) ont utilise des echosondeurs a faisceau unique de 38 kHz et de 200 kHz. Une partie de la retrodiffusion acoustique est attribuee au krill antarctique, d'apres les resultats des echantillonnages au filet et les observations a la video sous-marine et a laide d'un algorithme de classification acoustique a frequences multiples. La densite de biomasse annuelle moyenne du krill dans la zone de chantillonnage varie de 11 a 84*g[m.sup.-2]. Nous comparons nos resultats a ceux des inventaires acoustiques de densite de biomasse du krill realises durant les me mes annees dans la region occidentale de la mer de la Scotia par le programme americain ≪ Antarctic Marine Living Resources ≫ (AMLR). Les densites de biomasse du krill pres de la cote sont uperieures (test de t, p < 0,05), plus stables et leurs coefficients de variation plus petits que dans les inventaires beaucoup plus etendus de l'AMLR. La competition accrue entre les phoques, les manchots et les humains pour la ressource de krill cotier, surtout durant les mois delete austral, pourrait affecter le succes du recrutement deces predateurs de krill venus du continent. Nous discutons des implications de la biomasse du krill cotier sur les unites de gestion a petite echelle. [Traduit par la Redaction], Introduction Antarctic krill (Euphausia superba) are the main food resource for many of the fish, seabirds, and marine mammals in the Southern Ocean ecosystem. In addition to its ecological importance [...]

Marine sportfishing in southern California is a huge industry with annual revenues totaling many billions of dollars. However, the stocks of lingcod and six rockfish species have been declared overfished [...]

Echosounders may be calibrated by suspending a solid metal sphere in the acoustic beam and adjusting the system gain so that the measured target strength (⁠ T S ⁠) equals the theoretical value for the sphere. The suspension apparatus (i.e. net bag or loop of line glued into a hole, and control lines) may appreciably scatter sound, potentially affecting the sphere-echo intensity and phase, and hence the calibration uncertainty. Here, we characterize the effects of conventional suspension materials and configurations on measurements of sphere T S and recommend approaches to mitigate the observed effects on echosounder calibrations. We show that the effects of suspension lines on both calibration accuracy and precision change with line type and increase with line diameter and acoustic frequencies above ∼100 kHz. Compared to commonly used polyamide (nylon) line, ultra-high-molecular-weight polyethylene (PE) line has an acoustic impedance closer to that of water and therefore has a lessened effect on measurements of sphere T S ⁠. The effects may be mitigated in a practical manner using a 0.38-mm diameter, multifilament, PE line for the suspension. [ABSTRACT FROM AUTHOR]

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 (LT), fork (LF,) and standard lengths (LS) 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. Major‐axis regressions were used to calculate reciprocal length‐measurement conversions (e.g., LT to LS and LS to LT) and generalised linear models and ordinary least‐squares models were used to create MLRs that account for seasonal variations. The MLR models indicated seasonal differences for all species except C. pallasii, for which there was no multi‐season data. Discrepancies between these and published models were examined, along with the suitability and benefit of the various types of models used for length‐measurement conversion and MLRs. [ABSTRACT FROM AUTHOR]

This paper presents measures of target strength (T S ;   d B   r e   1   m 2) and models of T S vs. fork length (L ; cm), i.e. T S = 20 l o g L + b 20, for skipjack tuna associated with fish aggregating devices (FADs) in the Central Pacific Ocean. Measurements were made using 38-, 120-, and 200-kHz split-beam echosounders on a purse-seine workboat during fishing operations. To mitigate potential bias due to unresolved targets, T S measurements were rejected if they were not simultaneously detected with multiple echosounder frequencies in approximately the same location. The filtered TS and concomitantly sampled L data were used to estimate b 20 = −76, −71, and −70.5 dB for 38, 120, and 200 kHz, respectively, using the method of least squares. For comparison, quasi-independent estimates of TS and b 20 were calculated from acoustic echo-integration and catch data representing entire aggregations around the FADs. The results differed by ≤1 dB for all three frequencies. The sensitivities of these results to variations in fish morphology and behaviour were explored using a simulation of T S for fish without swimbladders. The utility of the results on acoustic properties of skipjack tuna and next research steps to achieve selective fishing at FADs are discussed. [ABSTRACT FROM AUTHOR]