Fig 3
Diagrammatic view of offset and tilt angles used when applying the tag to the dorsal surface of spawning chum salmon.
Source publication
A microcontrolled fish tag which records post-tagging life span, was developed and tested as a prototype. The method of making the tag and the results of tank test trials on chinook salmon (Oncorhynchus tshawytscha) and field trials on chum salmon (Oncorhynchus keta) are presented. This tag was specifically designed to measure survey life (SL) but...
Citations
... Life span or death tags are also needed that indicate where and when a fish becomes immobile, is eaten, dies, or its heart rate stops. Data-recording tilt tags are being developed that show when a fish tilts or goes belly up (Shardlow et al. 2007). A tag that sends out a strong "death throe" when this happens that could be recorded by a distant receiver is needed. ...
Most reviews of salmonid escapement estimation techniques have been based on logistical considerations or site-specific applications and not on statistical first principles. We reviewed six categories of salmon escapement techniques: area-under-the-curve, carcass abundance, mark-recapture, passage count, peak count, and redd count methods, based on statistical accuracy (i.e., unbiasedness), precision, and the ability to meet model assumptions. Within each of these categories of escapement techniques, we make recommendations on the best approaches to use for valid estimates and suggest five considerations when selecting an escapement estimation method. Currently in the Pacific Northwest, peak spawner counts are the most commonly employed technique and least defensible on a statistical basis than other methods. We recommend statistical accuracy and precision be given higher consideration when monitoring often increasingly scarce salmon resources.
Estimation of escapement for steelhead trout (Oncorhynchus mykiss) from periodic visual counts of spawners is complicated by extreme changes in observer efficiency over the migration period, low numbers of fish, pulsed arrival timing, and variable survey life. We present a maximum likelihood method to compute escapement and uncertainty that accounts for these difficulties using markrecapture data from radiotelemetry and snorkel surveys. Estimates of escapement were highly sensitive to assumptions about arrival dynamics and survey life, moderately sensitive to the assumed ending date of the run, and insensitive to assumptions about the form of observation error. Discharge and diver visibility explained between 69 and 78% of the variation in observer efficiency. Simulations revealed that declines in observer efficiency over the duration of the run increased bias and variability in escapement estimates but that this can be mitigated to a limited extent by increasing the number of surveys. The simulations also provided evidence that our likelihood approach was superior to the standard area-under-the-curve method for computing escapement when estimates of the numbers present over time are affected by substantial sampling error.
Estimating salmon escapement is one of the fundamental steps in managing salmon populations. The area‐under‐the‐curve (AUC) method is commonly used to convert periodic aerial survey counts into annual salmon escapement indices. The AUC requires obtaining accurate estimates of stream life (SL) for target species. Traditional methods for estimating SL (e.g., mark–recapture) are not feasible for many populations. Our objective in this study was to determine the average SL of chum salmon Oncorhynchus keta in the McNeil River, Alaska, through radiotelemetry. During the 2005 and 2006 runs, 155 chum salmon were fitted with mortality‐indicating radio tags as they entered the McNeil River and tracked until they died. A combination of remote data loggers, aerial surveys, and foot surveys were used to determine the location of fish and provide an estimate of time of death. Higher predation resulted in tagged fish below McNeil Falls having a significantly shorter SL (12.6 d) than those above (21.9 d). The streamwide average SL (13.8 d) for chum salmon at the McNeil River was lower than the regionwide value (17.5 d) previously used to generate AUC indices of chum salmon escapement for the McNeil River. We conclude that radiotelemetry is an effective tool for estimating SL in rivers not well suited to other methods.
Received July 21, 2010; accepted January 9, 2011
