Precipitous declines in pinto abalone (Haliotis kamtschatkana kamtschatkana) abundance in the San Juan Archipelago, Washington, USA, despite statewide fishery closure

Pinto abalone ( Haliotis kamtschatkana kamtschatkana ) index stations in the San Juan Archipelago were systematically monitored by the Washington Department of Fish and Wildlife from 1992 through 2006. During this period, abalone abundance declined by 77% and the mean shell length (SL) increased 10.4 mm. Abalone densities at all index stations are currently well below the threshold of 0.15 abalone·m–2 required for successful fertilization. From 1992 to 1996, 16% of individuals encountered measured <90 mm SL, while only 6% of the individuals from 2003 to 2006 were in this small size class. Similarly, the number of those >114 mm SL was greater in the 2000s than in the 1990s. The mean SL of all live abalone observed in the 1990s (107.62 ± 0.87 mm) was significantly different from the mean SL of empty shells (114.21 ± 2.1 mm), but no difference was detected between the mean SLs of empty shells and live abalone in the 2000s (114.97 ± 1.42 mm). Taken together, these data suggest recruitment failure from an Allee response to low population densities.

Season and Body Size Influence Movement of Hydropsychid Caddisfly Larvae (Trichoptera: Hydropsychidae)

Movement patterns of fifth-instar Hydropsyche slossonae larvae were investigated in artificial streams. In the first choice experiment, larvae were released into a central area and their upstream or downstream crawling or drifting was monitored. A second experiment used the same design; however, fifth instars collected during spring and fall were divided into two, nonoverlapping, relative size-classes (large and small) to determine how these factors influenced movement parameters. In both experiments, larvae always drifted more frequently than they crawled, but in experiment 2, drifting tendency declined with increasing weight in spring. In both experiments, there was no statistically detectable directional bias to crawling nor change in relative crawling direction with season or size-class. In experiment 2, drifting larvae were lighter than nondrifting larvae in the large size-class, but equal in weight in the small size-class. This result was unrelated to absolute weight, as large size-class larvae in fall were similar in weight to small size-class larvae in spring. It is possible that the relative weight differential of drifting and nondrifting larvae in one size-class but not the other may be related to sexual rather than body size differences.