1 million fish reveal translocation and captive-breeding synergies

The translocation described in this post could be an example of assisted migration although not in the sense that this is a climate change-motivated intervention. The movement of the Chinook salmon described by Holsman et al (2012) is assisting migration by transporting fish passed hydroelectric dams from the spawning headwaters to the ocean. As someone who has worked with threatened species and the small numbers of individuals this normally entails, I am envious of their sample size - over 1 million tagged fish made up the dataset and allowed an exceptional number of explanatory variables and interactions to be explored.


Key to their findings are the fact that their million fish represented wild and captively reared individuals, and translocated fish (moved down river) and non-translocated fish (in-river migrants) in all combinations over the period 1998 - 2006. They found that the origin of the fish and whether they were translocated around the hydropower schemes interacted synergistically on fish mortality: captive-reared fish benefited from being transported while wild fish were detrimentally affected by translocation. The latter occurred despite the fact that transportation should minimise deaths associated with migrating through hydropower systems.


The authors go on to explore a range of factors affecting survival in the marine environment before concluding with three important recommendations for management. Firstly, that the effects of management and environment can interact and this must be considered at the outset of any conservation programme. Secondly, that the survival translocated or captive-bred populations cannot be predicted from survival of wild populations because the intervention can alter some of the key phenological, behavioural, genetic and demographic parameters of a cohort. Thirdly, and I feel most importantly, practitioners should adopt an adaptive management approach. Whilst Holsman et al (2012) have the benefit of 1 million fish in their dataset, all translocation projects can improve the ability to identify and respond to unexpected and detrimental outcomes if translocated plants and animals are followed throughout the translocation programme on an individual basis.  As a systematic reviewer of plant reintroductions, I can vouch for this recommendation - survival analysis of an entire cohort is much more diagnostically powerful than samples of an already small population. However, I know it is easier said than done if you are say, trying to reintroduce a plant using seed, but it's not impossible and the rewards for the success of the project are more than worth it.

Holsman, K. K., Scheuerell, M. D., Buhle, E., & Emmett, R. (2012). Interacting Effects of Translocation, Artificial Propagation, and Environmental Conditions on the Marine Survival of Chinook Salmon from the Columbia River, Washington, U.S.A. Conservation biology : the journal of the Society for Conservation Biology, 26(5), 912–922. doi:10.1111/j.1523-1739.2012.01895.x