In‐Stream Egg Incubators Produce Hatchery Chinook Salmon with Similarities to and Differences from Natural Juveniles

Abstract

Supplementing fish populations at the egg stage is a low‐cost alternative to hatchery rearing that is presumed to improve adaptation to local natural conditions. The Shoshone‐Bannock Tribes began supplementing Chinook Salmon Onchorynchus tschwytscha in Panther Creek, Idaho, at the eyed egg stage in 2014. The Chinook Salmon eggs were artificially fertilized and reared to eye‐up in the hatchery and then planted in custom‐made in‐stream incubators (egg boxes) for volitional release and natural rearing. Using data from three brood years, we evaluated the efficacy of this supplementation program solely in terms of juvenile production. We related juvenile production to the placement and retrieval of the egg boxes, assessed the relative contributions of offspring (parr and emigrants) from the egg boxes (HOR) to overall juvenile abundance, and compared the performance (length, condition, dispersal distance, and survival) of HOR versus natural‐origin (NOR) juveniles. Brood year and box placement within the stream (distance upstream) were the best predictors of whether or not an egg box was retrieved from its original location. Meanwhile, the condition of the box (i.e., intact, damaged, or missing) was the best single predictor of juvenile production. Supplemented eggs represented an estimated 42, 50, and 42% of the total egg deposition in Panther Creek in brood years 2014, 2015, and 2016, respectively. A parentage analysis revealed that the egg boxes accounted for 6, 22, and 35%, respectively, of the parr production for the respective brood years when the data were normalized to the estimated egg deposition—less than the egg‐to‐parr production that was estimated for natural redds. As fall parr, the HOR fish differed from the NOR fish in terms of their length and dispersal behavior, but they were of similar length and condition at their emigration from Panther Creek and exhibited no significant difference in downstream survival through the Federal Columbia River Power System (FCRPS). Collectively, our results provide useful insights to fisheries managers who are interested in initiating or refining egg supplementation programs.

Effects of egg stocking on density, distribution, and size of young‐of‐year brown trout (Salmo trutta) in a large boreal river in northern Sweden

“…Our results suggested that egg stocking density increased dispersal of YOY trout from the stocking site, which was consistent with previous studies of brown trout and Atlantic salmon (Einum & Nislow, 2005;Einum et al, 2011;Eisenhauer et al, 2020;Elliott, 1984Elliott, , 1986Elliott, , 1994Milner et al, 2003) and chinook salmon (Oncorynchus tschwytscha; Conley et al, 2020). In contrast, we found that YOY although the negative sign of the correlation aligned with earlier studies of brown trout and Atlantic salmon fry (Einum et al, 2008(Einum et al, , 2011Eisenhauer et al, 2020;Elliott, 1984).…”

Evaluating Remote Site Incubators in Michigan Streams: Implications for Arctic Grayling Reintroduction

“…In conclusion, our field study demonstrated that RSIs can be used successfully in Michigan streams, building on previous research that has predominately focused on the western USA (Kaeding and Boltz 2004;Arnold et al 2017;Conley et al 2020). We found that removing dead eggs during incubation can effectively reduce the spread of fungus and increase the hatching success in RSIs, especially when RSI flow rate was low.…”

“…Sedimentation of RSIs was not an issue during our study, suggesting that RSIs may provide an alternative to in-stream incubation techniques at locations where sedimentation is high. Although the method of incubation used by managers is likely to be a function of both watershed characteristics and supplementation goals (Conley et al 2020), comparing the hatching success of RSIs to other stream incubation techniques (e.g., Jordan-Scotty incubators [Purchase et al 2018]) in future studies could provide useful information for managers working to restore native stream fishes.…”

“…Remote site incubators were developed in the western USA for the incubation of Pacific salmon Oncorhynchus spp. (Wampler and Manuel 1992;Conley et al 2020) and have since been used for restoration of other salmonids (Kaeding and Boltz 2004;Arnold et al 2017). Although RSIs have been used to incubate salmonids since the late 1980s, few studies have systematically evaluated their use.…”

Parentage-based tagging improves escapement estimates for ESA-listed adult Chinook salmon and steelhead in the Snake River basin

“…In both of the above modeling approaches, failing to account for unmarked, untagged hatchery-origin fish would lead managers to conclude that natural-origin populations were higher than the actual escapement ( Table 3) the South Fork Salmon River (Matala et al 2012), and many of these releases had no distinguishing marks or tags. Additionally, egg box programs, in which hatchery-cultured eggs are placed into in-stream incubators (LSRCP 2019), have been used in tributaries of the Salmon River to reestablish extirpated populations (Conley et al 2020). It is worth noting that unmarked, untagged fish could also be the byproduct of tag loss, imperfect tag detection, fin misclipping rates, or some combination thereof, and that these factors may vary by hatchery.…”