1 Final Report Period covered by Report: 05/01/2013 – 9/27/2015 Sea Scallop Research NOAA Grant Number: NA13NMF4540017 Start Date: 5/01/2013 End Date: 9/27/2015 Project Title: Survey of persistent scallop aggregations and an examination of their influence on recruitment using the FVCOM oceanographic model Investigators: Kevin D. E. Stokesbury, Ph.D. Bradley P. Harris, Ph.D. Changsheng Chen, Ph.D. Pingguo He, Ph.D Liuzhi Zhao, Ph.D. Address: School for Marine Science and Department of Environmental Technology Science University of Massachusetts Dartmouth Alaska Pacific University 200 Mill Road, Suite 325 4101 University Dr. Fairhaven, MA 02719 Anchorage, AK 99508 Email: [email protected] [email protected] Amount: We were granted 101,933 lbs ($993,844) for research and compensation. 2 Introduction Project Objectives: We intensively video surveyed 13 persistent scallop aggregations on Georges Bank, 11 of which are in closed areas including: Nantucket Lightship, Closed Area I and Closed Area II Access Areas, and the Habitat Area of Particular Concern (HAPC) in the northern portion of Closed Area II. We then used the FVCOM to examine scallop zygote dispersion using these persistent aggregations as source beds. In the proposal we had stated two extreme recruitment events have been observed in the last decade, the first providing extreme recruitment in the Mid- Atlantic in 2003 (probably the 2001 year class) and the second in 2009 providing extreme recruitment in the central portion of the Gulf of Maine and along the northern edge of the great south channel and Georges Bank. However, in 2013-14 we observed a third extreme recruitment event and have added that to the analysis as well. The environmental conditions related to these three events were examined with the FVCOM. The working hypothesis was that specific environmental conditions enabled increased fertilization success producing a scallop larval “cloud” which was carried by currents to Mid-Atlantic, Gulf of Maine and Georges Bank. This research is based on Sinclair’s Member-Vagrant theory where the persistent aggregations allow closure of the life cycle and vagrant zygotes produce high abundance when environmental conditions favor settlement over suitable habitat (Sinclair 1988). Determining these dynamics is fundamental to understanding how the sea scallop resource rebuilds and sustains it’s abundance to support the fishery. Methods Video Survey: Temporally persistent high scallop concentrations were identified previously by Harris (2011) using the annual video survey data from 1999 to 2010 (Figure 1). These aggregations were validated with input from the commercial scallop industry (for a complete description and references refer to Harris 2011). The proposed stations were sampled between June and July 2013. Using a multi-stage systematic design, we conducted a high resolution video survey of 846 stations in 13 specific areas of Georges Bank (Figure 2). The stations were separated by approximately 1 km (Figure 2). The SMAST sampling pyramid, supporting four cameras and eight lights, was deployed from a commercial fishing vessel (Stokesbury 2002, Stokesbury et al. 2004; Figure 3). A mobile studio including monitors, DVD recorders, DVRs and laptop computers for data entry and survey navigation (software integrated with the differential global positioning system) was assembled in the vessel’s wheelhouse. The vessel stopped at each pre-determined station and the pyramid was lowered to the sea floor. Two downward facing video cameras mounted on the sampling pyramid provide 2.84 m2 and 0.60 m2 quadrat images of the sea floor (Stokesbury 2002; Stokesbury et al. 2004). Another video camera, mounted parallel to the seafloor, provides a side profile of the quadrat area to aid in species identification. Lastly, a high-resolution digital still camera (12.3 megapixels) collects a single frame image of 1.06 m2 used to identify seed and juvenile scallops, verify species identification, habitat characteristics and sea scallop shell height measurements. Footage of the first quadrat is recorded and then the pyramid is raised so the sea floor can no longer 3 be seen. The vessel drifts approximately 50 m and the pyramid is lowered to the sea floor again to obtain a second quadrat; this is repeated four times. Sampling four quadrats at each station increases the sampled area to 11.36 m2. Figure 1. Map showing the 13 persistent aggregations on Georges Bank, 11 are located with the closed areas overlaid on the high resolution substrate map (Harris and Stokesbury 2010; Harris 2011). These aggregations contained 20 to 30% of all scallops in Georges Bank between 2003 and 2009. Persistent aggregations are outlined in black with abbreviated names. Nantucket Shoals – North and –South (NS-N, NS-S), Asia Rip (AR), Nantucket Lightship (NL) – South (NL-S) and East (NL-E), Hambone (HB) –South (HB-S), -West (HB-W), East (HB-E), Northern Edge (NE), and Southeast Parts (SEP), -South (SEP-S). The Georges Bank groundfish Marine Protected Areas (NLCA), Closed Area I (CAI), and Closed Area II (CAII). The hashed areas are rotational scallop fishery access zones. 4 Figure 2. Locations of the 846 stations sampled by the SMAST video survey from June to July 2013. The camera view area was increased to account for scallops that lie on the edge of the image. This expansion was reviewed and accepted in the 50th SAW and is based on the average shell height of scallops in the area. The length and width of each image was increased by the mean shell height of measured scallops within the survey area using the equation: (1) 퐸푥푝푎푛푑푒푑 푉푖푒푤 퐴푟푒푎 = (푙 + 푆퐻̅̅̅̅) × (푤 + 푆퐻̅̅̅̅) where l and w are quadrat length and width and 푆퐻̅̅̅̅ is mean shell height (O’Keefe et al. 2010). Figure 3. SMAST Video survey pyramid including 8 lights, 3 DeepSea video cameras, a 12.3 megapixel digital still camera and the area of each quadrat. Video footage of the sea floor was recorded on DVDs and onto a DVR. For each quadrat the time, depth, number of live and dead scallops, and latitude and longitude was recorded. After each survey the video footage was reviewed in the laboratory and a still image of each quadrat was digitized and saved. Within each quadrat, macroinvertebrates and fish were counted and the substrate was identified (Stokesbury 2002). When possible fish and macroinvertebrates were identified to species, otherwise animals were grouped into categories based on taxonomic orders. Counts were standardized to individuals m-2. Sponges, hydrozoa/bryozoa and sand dollars were recorded as present or absent within each quadrat. Sediments were visually identified following the Wentworth particle grade scale from the video images, where the sediment particle size categories are based on a doubling or halving of the fixed 5 reference point of 1 mm; sand = 0.0625 to 2.0 mm, gravel = 2.0 to 256.0 mm and boulders > 256.0 mm (Lincoln et al. 1992). Gravel will be divided into two categories, granule/pebble = 2.0 to 64.0 mm and cobble = 64.0 to 256.0 mm (Lincoln et al. 1992). Shell debris was also identified. Mean densities and standard errors of scallops were calculated using equations for a two-stage sampling design (Cochran 1977): The mean of the total sample is: n xi (2) x i1 n where n is the number of stations and xi is the mean of the 4 quadrats at station i. The SE of this 2-stage mean is calculated as: 1 2 (3) S.E.(x) (s ) n n 2 2 where: s (xi x) /(n 1) . According to Cochran (1977) and Krebs (1989) this simplified version of the 2-stage variance is appropriate when the ratio of sample area to survey area (n/N) is small. In this case, thousands of square meters (n) are sampled compared with thousands of square kilometers (N) in the study areas. All calculations use number of scallops per square meter. The absolute number of scallops in the survey areas is calculated by multiplying scallop density by the total area surveyed (Stokesbury 2002). Estimates of scallop meat weight in grams (w) were derived from shell height (mm) frequencies collected during each survey and shell height to meat weight regressions used in the 50th SAW. The mean meat weight for each 5 mm size bin was multiplied by the total number of scallops in the survey area to estimate the total biomass of scallop meats. Exploitable biomass was calculated using the commercial scallop dredge selectivity equation determined by Yochum & Dupaul (2008). Scallop Concentration The scallop concentration (Ca) in each survey station was calculated following Orensanz et al. (1998): 푄 2 ∑ 푛푖 퐶 = 푖=1 , 푎 푁 where Q = number of quadrats (4) at each station, ni is the number of scallops in quadrat i, and N is the total number of scallops at the station. Therefore, Ca gives the mean number of scallops experienced by each individual scallop in the four 2.84 m2 quadrats and thus has units of scallops per scallop (Orensanz et al. 1998). For simplicity we will give Ca in scallops. The Ca values 6 sampled each year were interpolated to a standard 1-km raster grid using Sibson’s Natural Neighbor method (Sibson 1981, Harris and Stokesbury 2010). Habitat Conditions The sediment characteristics were extracted from the Harris and Stokesbury (2010) maps of surficial sediment dominance, coarseness, heterogeneity and maximum type. In addition, we determined the degree of spatial correspondence between aggregations with the glacial-lag gravel outcrops mapped by Harris and Stokesbury (2010). Water depth (z) in the study area was mapped to the 1-km raster grid using 401,793 depth sounding records queried from the USA National Ocean Service data portal (www.ngdc.noaa.gov.html) with Sibson’s Natural Neighbor interpolation method (Sibson 1981).