Time of day affects squid catch in the U.S. Illex illecebrosus squid fishery

Abstract A mid-water otter trawl fishery targeting Illex illecebrosus operates in the northwestern Atlantic Ocean. The majority of I. illecebrosus are captured during mid-June to early September. Diel migratory behavior limits the fishery to daylight hours, but does the time-of-day affect catch? Illex illecebrosus were collected from each tow from a subset of the trawler fleet fishing on the outer continental shelf of the Mid-Atlantic Bight over the fishing season to determine the influence of time-of-day on catch. The male-to-female ratio was not influenced by time-of-day of capture. The size-frequency distribution of I. illecebrosus varied between tows within the same day of capture. Time-of-day of capture influenced average weight and, to a lesser degree, mantle length. Shorter and lighter squid were caught in the middle of the day. Larger and heavier squid were caught during the morning and afternoon. Data collection on commercial fishing vessels required that squid be frozen onboard, thawed onshore, and then weighed and measured. Differences between fresh and frozen squid were significant, but small, which permitted combining fresh and frozen measurements from different boats to track temporal and spatial trends in squid size. As time-of-day differences in catch were significant, obtaining unbiased size data from fishing vessel-based reports requires that samples be collected from the morning, afternoon, and evening tows during the trip.