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Fisheries Behavioral Ecology - Recent Student Internship Projects

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Student setting up a habitat experiment. Inia Mariel Soto (2003)
University of Puerto Rico

Project: Affinity by English sole for emergent benthic structure

Advisor: Cliff Ryer

Little is known about the essential fish habitat of many commercially important species. Flatfishes are generally regarded as selecting benthic habitats on the basis of temperature, sediment grain size and depth. In this study, intern Inia Mariel Soto examined whether juvenile English sole demonstrate preference for benthic habitats that contain emergent structure (shell, sponge, seagrass).

Bar graph of resultsWhen given the choice between a structured habitat and bare sand (see slide image above), juvenile English sole consistently demonstrated a preference for structured habitat. Interestingly, more is not always better; fish showed greater preference for structured habitats where the structural elements (e.g., sponge or eelgrass) were less dense. Although juvenile English sole seemed to demonstrate the strongest preference for eelgrass, a common feature in the estuaries where they reside, the extensive canopy characteristic of eelgrass beds seemed to have no effect upon this preference. Even when the eelgrass was trimmed to a height of 15 cm, compared to a normal height of 1 m or more, it was still attractive to juvenile fish, suggesting that structure close to the bottom is the characteristic preferred. Lastly, whereas many fishes show decreased association with refuge habitats when they are hungry, juvenile English sole deprived of food for 5 days continued to show the same preference for eelgrass as when they were recently fed. These finding, which provide evidence for the importance of emergent structure as a component of essential fish habitat for juvenile English sole, are being followed with field investigations.



Student conducting video analysis. Tara Duffy (2003)
University of Dayton

Project: Active patterns of juvenile rock sole

Advisor: Tom Hurst

Juvenile flatfishes use burial in the sediment and cryptic coloration as a means of reducing vulnerability to predation. However, habitat selection and prey search require movement exposing them to predators. Activity at night may reduce the risk of predation but results in less efficient foraging. As a result, the overall level and timing of activity undertaken by a juvenile flatfish represents a balance between the need to acquire food and avoid predators. Intern Tara Duffy examined the effect of feeding history on the activity patterns of juvenile northern rock sole.

PowerPoint slide showing rock sole experiment results.Feeding history has a significant effect on the level of and timing of daily activity in juvenile northern rock sole. The lines represent mean hourly activity of fish fed at different times as indicated by arrows, 9 a.m. (blue), 5 p.m. (red) and 9 p.m. (green). Observations were made in a 2.5 m tank backlit with infra-red illumination, allowing continuous monitoring of activity. In all cases, peak activity levels were observed under the intermediate light levels of dusk and dawn. Feeding resulted in a brief period of significantly increased activity. This was generally followed by an extended period of minimal activity, except among night-feeding fish where activity persisted. The extended activity of night-feeding fish may reflect a reduced feeding efficiency; hence fish required a longer time to reach satiation. Activity in light conditions was exclusively saltatory movement in contact with the sediment surface. At night, however, water column and surface swimming accounted for about half of total activity, independent of feeding time. Future work will examine the effectiveness of water column swimming in habitat choice and the predation consequences of this activity.



Student in the field. Lewis Barnett (2002)
Oregon State University

Project: Effect of ambient illumination on the behavioral response of juvenile English sole to disturbance by a bottom trawl footrope

Advisor: Cliff Ryer

Bar graph of resultsQuotas for commercially valuable fish species are often limited by “bycatch,” those fish that are inadvertently captured along with the target species. Understanding how fish respond to fishing gear under various conditions will aid in the design of fishing strategies and gears that reduce bycatch. In this study, intern Lewis Barnett examined how the presence or absence of light effect the behavioral response of English sole, Parophrys vetulus, to bottom disturbance caused by an approaching (trawl) foot-rope. More English sole responded early to the foot-rope in the dark (as opposed to letting the gear strike or pass over them) than do English sole in the light. This suggests that English sole will tend to be more vulnerable to capture by trawl gear at night than during the day, a result that needs to be confirmed through field experimentation.



Student holding camera sled. Nick Tagliavento (2002)
Oregon State University

Project: Comparison of divers, beam trawl and video camera sled in determining the abundance and habitat associations of juvenile flatfishes

Advisor: Al Stoner

Flatfishes are normally surveyed with towed fishing gear such as beam trawls and otter trawls. This kind of sampling gear is relatively easy to use but offers little opportunity for understanding critical relationships between fish and bottom features because fish are collected over the entire path of the trawl. Diver-based survey work can provide highly quantitative sampling and good characterization of the benthic environment, but diving is labor intensive and only small areas can be covered with limited underwater time and depth. An alternative is a towed camera sled, which can yield counts of fishes, a permanent video record of the fish and their habitats, and virtually unlimited bottom time.

Bar graph of resultsIntern Nick Tagliavento conducted preliminary studies in Yaquina Bay, Oregon, to perfect an inexpensive camera sled system and to compare densities of fishes and crabs estimated by divers, beam trawls, and camera sled. All three survey approaches were applied over the same 100 m long transects in locations known for juvenile flatfishes. First, it was determined that the sediment needed to be disturbed to provide accurate counts of age-0 flatfishes. A camera sled not equipped with a tickler chain produced density estimates that were a small fraction of those of a sled with a tickler chain. Subsequent comparisons showed that a chain-equipped camera sled yielded the highest density estimates for age-0 flatfishes, followed closely by estimates made by the divers. Densities determined from video tapes were 3-5 times higher than those from the beam trawl. Dungeness crabs were surveyed relatively well without a tickler chain, but very poorly with the beam trawl. Because of the permanent record of fish, invertebrates and habitat features provided in video tapes, a second generation camera sled is now used routinely by the Fisheries Behavioral Ecology Program for habitat-related surveys and field experiments in Kodiak, Alaska.



Student preparing an experiment. Adriana Veloza (2002)
East Stroudsburg University

Project: Effects of turbidity upon foraging by planktivorous juvenile marine fishes

Advisors: Alex De Robertis and Cliff Ryer

Turbidity, created by particulate materials suspended in the water column, can vary greatly both spatially and temporally in oceans and estuaries. This can affect the ability of many visual foragers to locate and capture food. In this study, intern Adriana Veloza examined how foraging by juvenile walleye pollock, Theragra chalcogramma, is effected by turbidity.

PowerPoint slide showing turbidity experiment results.Over the range of turbidities examined, there was little impairment of juvenile walleye pollock foraging for Artemia prey (see slide image at right). In contrast, available light had a much more significant effect. This same relationship has been observed in more recent investigations with other planktivorous species, suggesting that turbidity probably has little effect on foraging by fish that detect their prey at short distances (centimeters). Interestingly, concurrent studies demonstrated that piscivores, which detect their prey at greater distance (meters), are severely hindered by turbidity. They detect prey less frequently and have greater difficulty capturing prey when the water is turbid. This suggests that planktivores, which are often found in greatest numbers in the most turbid part of estuaries, may be seeking habitats where they are still able to feed, but are less vulnerable to predation.


Last updated 30 March, 2009

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