Paul D. Winger

Tilt angle and target strength: target tracking of Atlantic cod (Gadus morhua) during trawling

Vertical orientation (tilt angle) is known to affect the target strength (TS) of ensonified fish and is a large component of the variability inherent in acoustic-biomass estimates. To measure the effects of changes in tilt angle on TS during diel vertical migrations, a concentration of migrating Atlantic cod (Gadus morhua) was observed acoustically from a research vessel over several days. Single-target data were collected from a split-beam echosounder and were subsequently tracked, corrected for vessel orientation and movement, and analysed for 3-dimensional displacement (speed and direction). The results revealed a large variability in TS and several patterns of swimming behaviour from random to directed orientation and movement, with changes in both vertical and horizontal displacements and inferred orientation. These behavioural patterns and their affects on TS were analysed as a function of “time-since-sunset”. Regular diel orientation patterns were observed as cod rose from the ocean bottom in the evening, increasing their tilt angle, and descended at sunrise to regain the ocean floor. Standardized TS (B 20 ) was found to be highly correlated with tilt angle. This relationship can be used to correct for the diel changes in the TS of these migrating cod as a function of the in situ-measured tilt angle and thus to improve the accuracy of acoustic-biomass estimation.

Variable swimming speeds in individual Atlantic cod (Gadus morhua L.) determined by high-resolution acoustic tracking

Abstract Although several studies have determined swimming speeds for Atlantic cod (Gadus morhua L.) using acoustic telemetry, none have reported high-resolution tracking (high sampling frequency) for individual fish in order to obtain more accurate estimates of swimming speeds and to quantify within- and between-individual variation. In this study, in situ swimming speed of acoustically tagged Atlantic cod were recorded with high resolution (position fixing every 17 s) throughout the diel cycle during summer in a fjord in northern Norway using a stationary positioning system. The frequency distributions of swimming speeds are presented for individual cod (~30–60 cm). The high-resolution tracking technique revealed higher swimming speeds than previously reported for cod. Swimming speeds below 1.0 body lengths (bl) s−1 were most common (>70%), with only 4–7% of the recordings above the sustained swimming speed for this species. The observation that cod employed a blend of swimming speeds could reflect that searching for and capturing different prey types require a mix of swimming speeds.

Taking the bait: in situ voluntary ingestion of acoustic transmitters by Atlantic cod (Gadus morhua)

Voluntary ingestion of acoustic transmitters by Atlantic cod (Gadus morhua) was investigated under field conditions in the shallow inshore waters off Newfoundland. A surface-controlled tagging frame was used to suspend and monitor baited transmitters (16×45 mm up to 16×108 mm) near the seafloor at depths ranging from 12.5 to 39.0 m. The behaviour of cod toward the transmitters was quantified using an underwater video camera. Cod ranging in size from 11 to 92 cm approached and touched the transmitters. Both biting and ingestion were size-dependent. Eight successful taggings were completed with cod ranging in size from 34 to 92 cm. Transmitters deployed in the morning were consumed faster (mean soak time = 3.3 h) than transmitters deployed in the afternoon (mean soak time = 9.1 h). Tracking revealed that cod were active immediately following tagging, suggesting no effect of the tagging procedure. Individual fish were tracked for periods ranging from 5.6 to 18.8 d, with none of the fish regurgitating transmitters during the period for which they were tracked.

Artificial Light in Commercial Industrialized Fishing Applications: A Review

Abstract Fishing with an artificial light stimulus has existed for thousands of years. It started with simple techniques such as burning a large fire on the beach to attract fish, but over the centuries it has become increasingly technologically advanced. Today, the use of artificial light in commercial fishing plays a very important role in contributing to the total catch yield and economy of many industrialized fisheries. In most cases, fishing vessels employ lights at the surface, but more recently, low-powered LED lights installed directly on fishing gear have also become common. Using artificial light in commercial fishing applications appears to produce various outcomes and trade-offs (i.e., positive and negative effects). Positive benefits can include increases in catch rate, reductions in bycatch, and savings in energy, while negative effects can include ecological costs, overfishing, increased bycatch, production of plastic and marine litter, and greenhouse gas emission. This review provides an overview of fish vision in aquatic animals and the use of light in commercial industrialized fisheries, and provides discussion on potential solutions that strengthen the positive effects and minimize the negative effects of using artificial light in fishing applications.

Drop chain footgear: A new approach to environmentally friendly inshore Northern shrimp fishery in Newfoundland and Labrador, Canada

This study compared the effectiveness of a low seabed impact footgear versus a traditional rockhopper footgear on identical inshore Vónin shrimp trawls. The experimental trawl used in this study was designed to be low seabed impact through the reduction of contact area of the footgear by replacing traditional heavy rockhopper footgear with only a few drop chains lightly in contact with the seabed (i.e., drop chain footgear). Results from flume tank testing demonstrated that the trawls were similar in net geometry but the experimental trawl had a 62% reduction in contact area with the seabed compared to the control trawl. Comparative atsea fishing trials revealed that the drop chain footgear trawl has the potential to catch a similar amount of shrimp with appropriate drop chain rigging and modifications. Major by catch species (i.e., turbot, American plaice, and redfish) in terms of percentage of total catch in weight, quantities (i.e., counts), and size (i.e., length distribution) were not significantly different between trawl types. The experimental trawl had significantly lower resistance (i.e., warp tension) than the control trawl, however this did not translate into a detectable reduction in fuel consumption. Although the results are preliminary, this study demonstrated the potential and possibility of using drop chain footgear trawl for the Newfoundland and Labrador (inshore)Northern shrimp fishery. We recommended further studies that would lead to improve/optimize and eventually commercialize the drop chain footgear trawl as a low impact shrimp trawl choice in the province of Newfoundland and Labrador.