Assessment of River Herring Spawning Runs in a Chesapeake Bay Coastal Plain Stream using Imaging Sonar

Abstract

Recent declines in anadromous river herring (Alewife Alosa pseudoharengus and Blueback Herring A. aestivalis) have been documented in much of their range using fishery-independent spawning run counts. A lack of rigorous long-term run counts and demographic data for Chesapeake Bay spawning stocks resulted in the declaration of unknown stock status in a 2012 stock assessment and made it difficult to evaluate responses to conservation and restoration efforts. The objectives of the present study were to (1) conduct the first spawning run counts of river herring in the Choptank River, Maryland, since the run counts performed over a 2-year period in 1972 and 1973, (2) evaluate population structure and dynamics, and (3) identify environmental variables associated with run timing. Spawning runs of Alewives and Blueback Herring were recorded from March 10 to June 4, 2014, using imaging sonar and processed manually to produce hourly run counts of fish with TLs ranging from 200 to 350 mm. A total of 1,659,090 ± 91,250 fish with TLs of 200-350 mm (errors estimated using a CV of 5.5%) were estimated to swim upstream past the sonar unit. Boat electrofishing was conducted at weekly intervals to estimate species composition and obtain samples for demographic analysis. Using these species composition data to apportion run counts resulted in an estimated count of 581,275 ± 31,970 Alewives and 726,450 ± 39,955 Blueback Herring. Fish age by otolith analysis varied from 2 to 7 years and total instantaneous mortality (Z) was estimated at 1.47 (SE, 1.8 × 10 −5 ) for Alewives and 1.91 (SE, 1.1 × 10 −5 ) for Blueback Herring. Upstream migration occurred primarily in the afternoon and evening associated with increasing water temperature, and downstream migration occurred at low and decreasing levels of discharge. The present study established a new fishery-independent population monitoring effort for river herring in Chesapeake Bay and identified associations between environmental drivers and upstream and downstream movements.

Manual fish length measurement accuracy for adult river fish using an acoustic camera (DIDSON)

“…Although automatic analysis techniques have improved, manual processing is still the usual method to count and measure fish with DIDSON cameras within the scope of fish monitoring scientific surveys (Becker et al ., ; Crossman et al ., ; Doehring et al ., ; Lilja et al ., ; Ogburn et al ., ; Viehman & Zydlewski, ), but also in uses by different kinds of operators (for instance fish farmers, stakeholders, consultants, operators of once‐off surveys, etc .). Burwen et al .…”

“…Although automatic analysis techniques have improved, manual processing is still the usual method to count and measure fish with DIDSON cameras within the scope of fish monitoring scientific surveys (Becker et al, 2016;Crossman et al, 2011;Doehring et al, 2011;Lilja et al, 2010;Ogburn et al, 2017;Viehman & Zydlewski, 2015), but also in uses by different kinds of operators (for instance fish farmers, stakeholders, consultants, operators of once-off surveys, etc.). Burwen et al (2007Burwen et al ( , 2010 found a strong linear relationship (r 2 = 0.9) between manual DIDSON-based lengths and true lengths for a variable number of swimming fish at different ranges (i.e., distance to the camera).…”

Genetics and Juvenile Abundance Dynamics Show Congruent Patterns of Population Structure for Depleted River Herring Populations in the Upper Chesapeake Bay

“…One reason for the lack of response may be the bycatch in offshore fisheries, which was estimated at 727,400 Alewives and 1,069,000 Blueback Herring for the southern New England Atlantic Herring fishery during 2012-2013 (Hasselman et al 2016). This level of bycatch is substantial compared to the 2014 spawning run counts of 581,275 ± 31,970 Alewives and 726,450 ± 39,995 Blueback Herring in the largest documented Chesapeake Bay spawning run (Ogburn et al 2017) and other estimated run sizes in the region (ASMFC 2012). There may also have been insufficient time for the population to recover, or juvenile abundance indices may be relatively insensitive to changes in adult populations.…”

“…These differences in run timing MANAGEMENT BRIEF are consistent with spawning run counts in which both Alewives and Blueback Herring tend to arrive 1-3 weeks earlier in eastern shore tributaries (Choptank and Nanticoke rivers) than in upper western shore tributaries (Patapsco and Susquehanna rivers; M.B.O, unpublished data). Stream temperature is one important driver of spawning run timing for river herring (Ellis and Vokoun 2009;Ogburn et al 2017), but other mechanisms potentially driving observed differences in run timing are poorly understood. Temporal shifts in the genetic composition of river herring spawning runs in Chesapeake Bay tributaries warrant further attention and will require weekly sampling in more rivers and multiple years to determine whether it is a common phenomenon potentially explaining observed patterns of genic and genetic differentiation.…”

“…The potential for stock structure among Chesapeake Bay tributaries has important implications for the design of conservation, management, and monitoring strategies. Fishery-independent monitoring of Chesapeake Bay spawning streams has been limited primarily to juvenile abundance indices (ASMFC 2012), but there is increased interest in developing comprehensive monitoring of adult spawning populations (Ogburn et al 2017). However, there is insufficient information for evaluating the number and distribution of spawning runs that should be monitored to adequately characterize population dynamics within the Chesapeake Bay.…”