The vertical movement patterns of eight Swordfish Xiphias gladius from 109- to 249-cm lower jaw fork length in the western North Atlantic were studied utilizing pop-up archival transmitting tags. Deployments ranged from 120 to 151 d. Swordfish demonstrated significant differences in depth and temperature distributions between daytime and nighttime periods. Individual Swordfish behavior was characterized by occupying surface waters of less than 100m during the night and depths greater than 400m during daytime hours, vertical movements between the surface and depth occurring during crepuscular hours. The maximum depth recorded was 1,448m (one of the deepest recorded depths for the species). Daytime surfacing behavior was seen in all tagged Swordfish, a rare finding for Swordfish in tropical latitudes. A dominant diurnal period of 1 cycle/d was found from a power spectral density analysis of five of the tagged Swordfish, a novel method for determining periodicity in the behavior of tagged animals. Regression analysis indicated a significant positive relationship between depth and fraction of the moon illuminated, supporting anecdotal and vessel logbook information from local Swordfish fisheries indicating changes in depth in relation to lunar phase. Received January 17, 2012; accepted August 5, 2012

Herring (Clupea pallasii and C. harengus) have been observed to release gas from their bladders during vertical migration likely to adjust buoyancy and also when under strong predation pressure. Based on recently measured and modeled sound for individual fish, spectral levels are estimated for entire herring schools in the ocean for both scenarios, and the feasibility of passive detection is explored. For a typical school of migrating herring near-surface spectral levels of about 50 dB rel., 1 microPa radical Hz at 3-7 kHz are predicted. If wind conditions are calm where migrating herring are found, such as for Pacific herring in Prince William Sound, Alaska, passive detection is very likely. For an exemplary 10 metric ton compact school, peak spectral source levels of about 80-90 dB rel. 1 microPa radical Hz ref. 1 m are predicted, yielding a range of detection against calm wind background of about 1000 m. Field measurements of potential gas-release events agree with the predictions for the compact school scenario with regard to levels and spectral shape and indicate that passive acoustic monitoring is feasible and could be a prime tool to study predator-prey interactions.

Thorne, R. E., and Thomas, G. L. 2008. Herring and the "Exxon Valdez" oil spill: an investigation into historical data conflicts. - ICES Journal of Marine Science, 65: 44-50.It was generally believed that the 1989 “Exxon Valdez” oil spill did not cause the collapse of the Prince William Sound Pacific herring (Clupea pallasi) population because of a 4-year gap between the spill and the collapse. However, we noted in a previous paper that some data suggested an earlier timing for the herring decline. We examine historical patterns of herring spawn, anomalies in historical fisheries model predictions, changes in predation behaviour of Steller sea lions (Eumetopias jubatus), and a decadal database of acoustic measurements of herring biomass. Behaviour of adult herring makes them especially vulnerable to damage from oil spills, something that was either unknown or misunderstood at the time of the spill. We therefore argue that the start of the herring decline was coincident with the oil spill, and that the decline took place over a 5-year period, rather than the single-year collapse previously reported. Although a comprehensive management approach is now in use for herring, the tools were not in place at the time of the oil spill or the subsequent collapse.

High-frequency acoustic surveys over the past 15 years show that the trophic structure in Prince William Sound (PWS), Alaska, functions as a wasp-waist ecosystem. Three dominant biomasses in PWS are: (1) Pacific herring (2) walleye pollock and (3) the large-bodied copepods (Neocalanus spps.) that dominate the spring zooplankton assemblage. The acoustic surveys and associated ecosystem observations suggest that the relative dominance of herring and pollock affects the composition of the apex predators. The near-shore and near-surface distribution of herring provides access by surface-oriented marine mammal and seabird predators, such as sea lions, seals, murres and cormorants, to a crucial winter-period food source. In contrast, the deep, off-shore distribution of the pollock favors large benthic predators, such as demersal sharks, halibut, and flounder. The acoustic surveys also demonstrated that the abundance of large-bodied copepods in PWS is critical to ecosystem productivity, including survival of juvenile pink salmon, and may affect the relative dominance of herring and pollock. An additional outcome of the long-term database on Pacific herring was the discovery of linkages between the 1989 Exxon Valdez oil spill and a subsequent collapse of the herring along with associated predators.

Passive acoustic detection and monitoring of various marine fishes has recently received much attention in the literature. It has been recognized that passive acoustic techniques have the potential to complement traditional active acoustic surveys and to significantly increase their overall efficiency, if the acoustic signatures of the considered species are well understood. In this paper, the potential of passive acoustic techniques is explored for the specific case of Pacific herring (Clupea palassii). It is demonstrated that schools of herring can acoustically be detected by observing the sound of coordinated bubble release, triggered, e.g., by predator activity. This sound not only has identifiable features that can be exploited for determining the presence or absence by simple means, but could also carry abundance and size information. Work supported by ONR and the NMFS via the PWSSC.

Herring (Clupea pallasii and C. harengus) are known to release gas from their swim bladder to assist a number of complex behaviors, such as buoyancy adjustments and predator avoidance. The noise associated with the release has recently been reported in the literature and related to oscillating bubbles. Average source levels (SLs) of 73 dB with regard to microPa rms reference 1 m have been reported for bubbles produced by herring in the laboratory. A model is provided for predicting the SL in terms of the gas flow rate from the swim bladder into the bubbles. Based on these laboratory conditions, an inversion yields a rate of 0.9 (0.3-3.2) ml/min. Furthermore, the model predicts an acoustic SL of 89 (79-99) dB with regard to microPa rms reference 1 m for pulses emitted by herring in a natural shallow water environment at unknown distance corresponding to a flow rate of 2.5 ml/min. An analysis of published acoustic data suggests that herring is capable of controlling the gas flow and the corresponding acoustic levels over a wide range according to different behavioral needs. The proposed model allows an extrapolation of the laboratory results to situations that are relevant for bubble release of herring schools in the ocean.

The single most important information for the conservation of exploited marine fish stocks are precise measurements of their biomass so that harvest rates can be established that do not deplete the stock. However, the measurement of marine fish stocks is difficult due to the size, structure, and composition of the ocean, and the highly dynamic movements of the fish. Furthermore, traditional, discrete net sampling approaches have lacked sampling power to assess single fish stocks in time and space [2]. Without the ability to independently measure fish stock biomass with precision, managers have instead relied upon the commercial catch and deterministic indices as a primary source of empirical data. Also, without precise empirical data on stock biomass, the models used to make predictions are unverifiable and highly uncertain. Despite the severe management risks, this is the status quo, and it greatly confounds our efforts to sustain our fisheries, conserve exploited fish stocks and understand the dynamics of population response to natural and anthropogenic changes in the environment. High frequency active acoustics has been used to assess fish stocks for over four decades. When first introduced in the 1970s, there were hopes that acoustics would overcome the marine fish stock measurement problem because of a 105 increase in sampling power. However, prior to the introduction of acoustics the management agencies had already chosen large ocean areas to survey fish stocks, specifically in the summer months when the weather was good. In doing so, the agencies had assumed that surveys in large ocean areas would allow a representative assessment of single stocks of fish.

Evidence of direct mortality to fishes exposed to oil is very limited. The 1989 Exxon Valdez oil spill had major impacts on marine mammals and seabirds, but was not implicated in the 1993 collapse of the Prince William Sound herring population because of the four year gap. However, we use several independent evidences, including changes in the predation behavior of Steller sea lions, to show that the collapse actually began in 1989. We show the failure to detect the actual timing of the collapse was due to deficiencies in the fishery model used to assess herring population abundance and lack of understanding about the vulnerability of herring. Finally, we show that the oil spill actually had greater impacts than originally believed as a result of catastrophic impacts on the ecosystem from the herring collapse

New insight into the feeding habits of these mammals will help conservation attempts.

ABSTRACT Since 1969, the authors have been involved in over 200 hydroacoustic surveys of fish populations in more than 25 lakes. These studies have included a variety of different species assemblages and objectives, although most, such as Lakes Washington and Ozette in Washington and Tustumena in Alaska, are sockeye salmon nursery lakes. The objectives of these studies have included fisheries management, evaluation of lake enhancement programs, or environmental impact. During the 14 years of these investigations, both the equipment and procedures have evolved and improved considerably. Earlier techniques were very limited in their ability to detect fish near surface or in shallow water and had very limited capabilty for size discrimination. Current technology has solved most of these problems. These developments and their capabilities are presented along with the results of surveys on lakes with a variety of biological and physical characteristics. The results include a considerable amount of “ground truth” data from other assessment techniques. In many cases these data are obtained from various net sampling techniques. However, some comparisons have revealed considerable biases with net sampling techniques which are associated with changes in light intensity, turbidity, or fish behavior.