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Determining the Timing and Location of Fish Spawning


Summary: The reproductive life history of fish, including when and where they spawn (=release of eggs from ovary), has been critical to the proper management of a fish species in the commercial fishery. To increase catch, commercial fishermen have historically focused on aggregations of fish at the time of spawning and, in response; management agencies have used this information to assign fishing limits in an effort to sustain populations. An important tool for the management of fish is the analysis of population structure using genetic markers. Results of the analyses of genetic population structure have critical impacts on the management of a species since they may mean the difference between managing a species as a single entity or as separate populations across their range. Genetic population analyses based on samples taken from the wild rely on the supposition that fish from discrete reproductive populations are known and being assessed separately. Yet, for many species of fish this assumption is clearly violated since their spawning sites are unknown and DNA samples for genetic analysis are taken without this information (e.g., sablefish - Jasonowicz et al., 2017). 54 For a few species, the timing and location of spawning is known. However, for many marine fish, particularly deep-water species, it is not. This includes some of the most commercially important species such as sablefish and Pacific hake. Even for species such as halibut where some reproductive information is available, our knowledge is incomplete. For species such as Pacific hake, spawning information is essential for their management since changing climateocean conditions are altering seasonal migratory behaviors (Benson et al., 2002; Ressler et al., 2007). These changes have been hypothesized to have altered the timing and locations of spawning and how this impacts the assessment of population size for this species is unclear. While there has been significant development of tagging technologies (e.g., archival and acoustic tags) to follow the general movements of fish and to discern their habitat (e.g. depth and temperature) preferences, there has been relatively little effort to develop technologies that could determine when and where a fish spawns. There has been some research using radio transmitters or acoustic telemetry tags that are inserted into the ovary (via the oviduct) with the hypothesis that when spawning and egg release occurs, the tag is expelled from the ovary and can be detected by a receiver in the environment. If one could locate the tag then the location (but not timing) of spawning can be inferred. In these studies, the general tag locations were made by manually searching shoreline areas with receivers to detect signals (Pierce et al., 2007; Skovrind et al., 2013), or an existing acoustic telemetry array was employed (Binder et al., 2014). However, in all of these cases, some a priori knowledge of where the spawning locations were located was necessary to either search for the tags or to determine where to locate the telemetry arrays. This approach may have some probability of success in a very limited space such as a freshwater lake or shoreline, but would be impossible in a large open body of water such as the ocean. In addition, these methods do not define the timing of spawning. Clearly, when dealing with species in the ocean that have wide distribution, radio transmitters or acoustic telemetry cannot be used for this purpose. Further, this would be even more difficult for fish species that reside in deep water that would be inaccessible to manual searching with receivers or for telemetry array deployment. The Problem: A technology is needed that can determine the precise timing of spawning (=release of eggs from the ovary) and to link that event to the simultaneous determination of the geographic location of that spawning event. We hypothesize that, depending on how this problem is addressed other uses for this technology could be envisioned such as the archiving of other types of data from the fish (see project goals).


Project Goals: To solve this problem, a successful technology would be one in which the release of eggs from the female could be determined, the timing of that release recorded, and that information could subsequently be obtained by a researcher. In addition, the technology would have to also determine the geographic location at which the release of the eggs occurred. The release of eggs from the ovary (signaling spawning) might be directly monitored or, indirectly monitored through the simultaneous release of something that could be placed in the ovary and be used as a proxy for egg release. The egg proxy could then be used as a signal itself or as a trigger that could then initiate other processes such as the release of a tag (e.g., satellite popup tag) 55 that is attached to the fish. That tag could then be used to transmit or contain the information on the time and location of egg release. From past studies, we know that proxies such as miniature radio transmitters or acoustic tags can be expelled from the ovary at the time of spawning. It is then a matter of how to link these proxies with other technologies that would record that information and relay it to the researcher. In developing this technology, no a priori knowledge of where and when the spawning will take place can be assumed and it is unlikely that the fish itself will ever be recovered. Rather, the information on when and where spawning occurs has to be transferred independently to the researcher from where it is collected and could, therefore, involve some form of satellite transmission. While the technology in this subtopic proposal is being directed at solving the issue of where and when fish spawning takes place, it could also be used for other purposes depending on how the problem is solved. The general concept of detecting and archiving what is occurring in a fish over some period of time and then eventually relaying that information to an individual (researcher or other), could have significant applications in physiology (detecting and recording various internal parameters such as blood pressure), behavior (sensing the movements of predators or other neighboring fish such as those in a school), or surveillance (detecting the presence or movements of other objects such as marine mammals or ships). The use would depend on what precisely is placed into the fish and what that device could record.

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