Using a baited camera to assess relative abundance of juvenile Pacific cod: Field and laboratory trials

Abstract

Juvenile fishes are sometimes difficult to survey because they occur in a variety of structurally complex habitats that are not readily sampled with traditional trawl or seine gear. Laboratory experiments and field sampling were conducted to determine whether a baited-camera system could be used effectively to survey age-0 gadids. Pacific cod ( Gadus macrocephalus Tilesius), saffron cod ( Eleginus gracilis Tilesius), and walleye pollock ( Theragra chalcogramma Pallas) all responded to bait bags presented in the laboratory, with increased general activity and approaches to the bait. Pacific cod responded most strongly, and remained in close proximity to the bait bag. In nearshore habitats of Kodiak, Alaska, age-0 gadids (mostly Pacific cod) were quickly attracted to a baited-camera system. Arrival rates stabilized within 15-min, and several metrics for Pacific cod abundance taken from the video records were closely correlated with the numbers collected in seine hauls. Highest correlations occurred with the total number of fish arriving in camera view during 15-min sets (NFA 15) and with the overall maximum number of fish observed at one time during the sets (MaxN O). The time for first arrival of fish in view (TFA) was not correlated significantly with the numbers of fish in seine collections. NFA 15 was also useful for age-1+ saffron cod. Occasionally, the presence of large fish had a negative effect on assessments of age-0 fish, but the impact was important only when the large fish were present continuously. The baited-camera system performed equally well in seagrass, kelp and open habitats, and can be used to rapidly assess the relative abundance of Pacific cod and selected other species in a wide range of habitats in shallow and deep water.