UC Davis UC Davis Previously Published Works Title Use of a hydrodynamic model to examine behavioral response of broadnose sevengill sharks (Notorynchus cepedianus) to estuarine tidal flow Permalink https://escholarship.org/uc/item/23q9c0bz Journal Environmental Biology of Fishes, 102(9) ISSN 0378-1909 Authors McInturf, AG Steel, AE Buckhorn, M et al. Publication Date 2019-09-15 DOI 10.1007/s10641-019-00894-3 Peer reviewed eScholarship.org Powered by the California Digital Library University of California Environ Biol Fish https://doi.org/10.1007/s10641-019-00894-3 Use of a hydrodynamic model to examine behavioral response of broadnose sevengill sharks (Notorynchus cepedianus) to estuarine tidal flow Alexandra G. McInturf & Anna E. Steel & Michele Buckhorn & Philip Sandstrom & Christina J. Slager & Nann A. Fangue & A. Peter Klimley & Damien Caillaud Received: 17 February 2019 /Accepted: 13 June 2019 # Springer Nature B.V. 2019 Abstract Innovative telemetry and biologging technol- hydrodynamic model of the estuary and calculated cur- ogy has increased the amount of available movement rent vectors along each track. We hypothesized that the data on aquatic species. However, real-time information sharks would adjust their swimming speed and direction on the environmental factors influencing animal move- depending on current strength when passing through the ments can be logistically challenging to obtain, particu- channel underneath the Golden Gate Bridge. Our results larly in habitats where tides and currents vary locally. indicate that sharks did tend to follow the current flow in Hydrodynamic models are capable of simulating com- the channel, but their overall displacement did not sig- plex tidal flow, and may thus offer an alternative method nificantly correlate with tidal amplitude. We conclude of contextualizing animal movement in coastal habitats. that the sharks may respond to environmental factors Here we use this tool to examine the influence of other than tidal flow, altering their movement at a finer tide on the movement of broadnose sevengill sharks scale than initially considered. Overall, this suggests that (Notorynchus cepedianus) in the San Francisco Bay hydrodynamic simulation models can be used to visual- estuary. Three sharks were actively tracked using acous- ize and quantify environmental factors that may affect tic transmitters for 3 to 4 days. We then generated a movement patterns in aquatic organisms. We recom- mend future studies combine these models with other biologging techniques to measure energy expenditure at A. G. McInturf (*) : A. E. Steel : M. Buckhorn : a finer spatial scale. P. Sandstrom : N. A. Fangue : A. P. Klimley Department of Wildlife, Fish and Conservation Biology, . University of California, Davis, CA, USA Keywords Active tracking Estuary Movement e-mail: [email protected] ecology. Environmental data P. Sandstrom Tacoma Public Utilities, 3628 South 35th Street, Tacoma, WA, USA Introduction C. J. Slager Animal movement is affected by a variety of factors, Aquarium of the Bay, Biological Programs/Conservation, Exhibits ’ and Educational Engagement, San Francisco, CA, USA including the animal s internal state, navigation and motion capacity, and the surrounding biotic and A. P. Klimley abiotic environment (Nathan et al. 2008). Among Petaluma, USA these, there has been increasing recognition that D. Caillaud external constraints in particular may play a larger role Department of Anthropology, University of California, Davis, CA, in shaping an organism’s movement path than previous- USA ly considered (Wilson et al. 2012; Shepard et al. 2013; Environ Biol Fish Brownscombe et al. 2017; Gallagher et al. 2017). In shark (Notorynchus cepedianus)movementsintheSan estuarine habitats, one such external force is the seasonal Francisco Bay estuary. We combine tidal current simu- and daily hydrological variance, which is generated by lations generated at a ~50 m resolution with active complex bathymetry and water flux from various in- tracking data from three sharks. In the estuary, sevengill shore and offshore sources (Brodersen et al. 2008; sharks show a preference for high-flow areas, such as Anderson and Beer 2009; Forsythe et al. 2012;Kelly the channel underneath the Golden Gate Bridge and Klimley 2012). Due to the presence and variability (Ketchum et al. 2017). We first hypothesized that of these currents, it is likely that different species that sevengill sharks would minimize energy expenditure reside in or transit through estuaries will exhibit plastic- by consistently moving in the direction of tidal flows ity in their movement in response to the currents. In to travel within the high-flow channel. Second, because some cases, currents may induce little to no active the San Francisco Bay experiences a mixed semi- response from aquatic organisms, while in others they diurnal tide, we predicted that this response would vary can be an impediment to the organism by deflecting the by current strength; specifically, that I) in slow currents animal off course (Chapman et al. 2011; Kelly and generated by weak tides, sharks would swim more ac- Klimley 2012). Currents can also be beneficial by re- tively in the direction of the current flow in order to ducing an individual’s travel time and energetic expen- move through the channel. In this case, the total dis- diture (e.g., Bernatchez and Dodson 1987; Kelly and placement of the shark during that tidal segment would Klimley 2012) or by increasing foraging opportunities be greater than that of the current along the shark’s (e.g., in upwelling areas; Benjamins et al. 2015). movement path; and ii) in faster currents resulting from Assessing the nature of behavioral response requires stronger tides, sharks would move passively within the an understanding of how the animal moves in the con- water mass while being transported through the channel text of the major environmental constraint in question. in the direction of the tide. The total displacement of the There has been recent attention to this area of research shark would then be equal to or less than that of the due to interest in dynamic management approaches, current. Our ultimate goal was to explore the use of which require repeated assessment or measurement of hydrodynamic models to determine the frequency with biological and environmental data to update manage- which the sharks moved in and out of the estuary with ment recommendations. These tools rely on environ- the tide, and whether the environmental tidal conditions mental datasets obtained via remote sensing to predict altered their mode of transport. animal location on a daily, regional scale (e.g., EcoCast; Hazen et al. 2018; Welch et al. 2019). However, real- time measurements of the more fine-scale environmen- Methods tal variables affecting organism movement patterns, such as current flow, can be logistically challenging to Study system obtain via remote sensing or direct field measurement (Benjamins et al. 2015). Thus, complementary methods The San Francisco Bay is the most geographically ex- may be necessary to contextualize animal movement pansive estuary along the California coastline, with a data and forecast species distribution at a local scale. surface area of 1240 km2 (Conomos et al. 1985). Tides Multi-dimensional hydrodynamic models are typi- are mixed and semidiurnal (i.e., two unequal high and cally used to investigate water movement, sediment low tides per day), with a high-flow channel where transport, and water quality for estuarine and coastal currents reach peak velocities (approximately 2.0 m/s; environments (Elias et al. 2001). These models can also Bennett et al. 2002) through the narrow passage under- provide information on localized currents in dynamic neath the Golden Gate Bridge (Conomos et al. 1985; aquatic habitats. In cases where empirical data from Ketchum et al. 2017). The mean tidal range is approx- buoys or remote sensors are missing, this tool could imately 1.7 m (NOAA, National Ocean Service 2019), therefore be utilized to quantify the environment and during the study period, tidal amplitude ranged from through which marine organisms move, offering greater 1.5–4.0 m. The mean depth of the entire estuary is less insight into the impact of environmental constraints. than 10 m, but the central channels (such as that beneath Here we explore the use of hydrodynamic models in the Golden Gate Bridge) can reach depths of over 100 m examining the influence of tide on broadnose sevengill (US Geological Survey 2014). The estuary also holds Environ Biol Fish several small islands. Relevant to this study, Alcatraz like many other mobile marine predators such as Island (.09 km2) is located approximately 2.9 km east of cetaceans, pinnipeds, and seabirds that exploit tidally the Golden Gate Bridge, while Angel Island (3.1 km2)is energetic environments for foraging opportunities approximately 4 km northeast (Fig. 1). It is also impor- (Benjamins et al. 2015;Lieberetal.2018). It is therefore tant to note that the estuary is highly urbanized and likely that their movements are affected by the prevail- impacted by numerous anthropogenic activities includ- ing tidal flow in the deep narrow channel underneath the ing channel dredging, freshwater diversions, watershed Golden Gate Bridge. modifications, urban run-off, and ship traffic (Barnard et al. 2013). Due to the complex shape and bathymetry Active tracking caused by the influence of both these anthropogenic and natural factors, the San Francisco Bay estuary is an area Three sharks were collected on a flood tide near a small in which tidal influence is not only highly variable but reef northwest of Alcatraz Island on 29 July, 9 September also heterogeneously distributed. It is thus an ideal and 14 October 2008. Each was caught using a baited location to examine how organisms respond to dynamic hook and netted to bring aboard the vessel. The shark was current flow. then placed in a tank filled with flowing seawater, was During the spring and summer, the San Francisco sexed and measured for total length (TL, meters), stan- Bay estuary serves as a foraging and pupping ground dard length (SL), and girth behind the pectoral fins.