Tag Archives: Chinook

Chinook salmon and southern resident killer whales occupy similar depths in the Salish Sea

New paper by UW colleagues entitled “Interpreting vertical movement behavior with holistic examination of depth distribution: a novel method reveals cryptic diel activity patterns of Chinook salmon in the Salish Sea” shows some results from Vemco receivers I deployed in the San Juan Islands. Young adult Chinook favor depths less than ~30 meters, with some seasonal variability in their diel activity patterns. Overall, they go deeper and vary more in the depths at night.

Dive profiles for two Salish Sea Chinook salmon during the summer and fall.

Dive profiles for two Salish Sea Chinook salmon during the summer and fall.

Interestingly, according to a report to NOAA/NWFSC by Baird et al, 2003 (STUDIES OF FORAGING IN “SOUTHERN RESIDENT” KILLER WHALES DURING JULY 2002: DIVE DEPTHS, BURSTS IN SPEED, AND THE USE OF A “CRITTERCAM” SYSTEM FOR EXAMINING SUB-SURFACE BEHAVIOR) SRKWs spend >97% of their time at depths of less than 30m.

This suggests any future deployment of horizontal echosounders should aim to ensonify a depth range centered on ~25m (e.g. 5-45m or 10-40 m).  Compared to the estimated orientation and surveyed depth range of our 2008-9 salmon-SRKW echosounder pilot studies, we may want to measure inclination more carefully to (a) center the survey on the mean summertime depth range of Chinook and (b) avoid ping reflections from surface waves, boats, and bubbles (which may have confused interpretations of targets >100 m from the transducer).  Here’s my diagram for the situation in 2008-9 in which we were centered on 15 m and ensonified a maximum depth range of ~0-30m (in other words, we may have been aiming a little high):

Screen grab from the 2009 ASA presentation showing echosounder geometry

Screen grab from the 2009 ASA presentation showing echosounder geometry