The East of Nantucket Survey. Preliminary Results Presented by Eric Powell to the Habitat PDT on September 14, 2017

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1 The East of Nantucket Survey Preliminary Results Presented by Eric Powell to the Habitat PDT on September 14, 2017

2 Thanks Roger Mann who handled the logistics of the cruise Tom Dameron and others who provided logistical support planning SCeMFiS (NSF Science Center for Marine Fisheries) who funded the project The science party of Mann, Kelsey Kuykendall, Jeremy Timbs, and Chase Long And especially the captain and crew of the F/V Mariette

Survey Design 63 stations Station grid design: Hub and spoke 3-nm spoke length Reposition criteria depth constraint state boundary closed area boundary

3 Survey Design 63 stations Station grid design: Hub and spoke 3-nm spoke length Reposition criteria depth constraint state boundary closed area boundary Reposition distance 1-nm search radius Survey Design Working Group area of concern Presentday closed area Northern portion proposed HMA NMFS survey grid 2 nm x 2.5 nm

4 Survey protocol 5-minute tow 99 in dredge Shaker closed to about 0.75 in Tow speed ~3 knots Tow coverage: ~1300 m 2 per tow, ~82,000 m 2 total All catch sorted Delaware II sorting protocol followed as closely as possible Deviation: bushel volume measurements used rather than counts for mussels Ten haphazardly chosen rocks, cobbles, boulders, shells photographed. Photos biased towards particle side with bionts, if present

5 Distribution of surfclams Surfclams found throughout the region except the offshore and southern portions of the HMA Largest numbers found in the north central portion of the HMA Zero catch stations not marked

6 Differential distribution: submarket (0-120 mm) versus small market ( mm) surfclams Surfclams <120 mm and surfclams mm are distributed almost identically Few small surfclams are found inshore Nearly all submarket and small market size clams are in the northcentral portion of the proposed HMA scale differs between data types Circle proportional to number per m 2 : mm : mm

Surfclams >170 mm and surfclams 150-170 mm are distributed almost identically Few large surfclams are found offshore Nearly all market size surfclams are east of or in the eastern portion of the

7 Surfclams >170 mm and surfclams mm are distributed almost identically Few large surfclams are found offshore Nearly all market size surfclams are east of or in the eastern portion of the proposed HMA Clams mm are biased south of the largest clams This is the largest concentration of very large (>170 mm) clams in the federal stock! scale differs between data types Circle proportional to number per m 2 Differential distribution: large surfclams : mm : >170 mm Nantucket survey: surfclams >170 mm over mm

8 Differential distribution: small versus large surfclams Large surfclams are distributed inshore of small surfclams with very limited overlap Recent recruitment is offshore Surfclams are moving into deeper water as observed throughout the range Suggested time frame for deep-water colonization: years scale differs between data types Circle proportional to number per m 2 : mm : mm

9 Differential distribution: surfclam shell versus large surfclams Large surfclams and shell overlap relatively consistently Surfclam shell is taphonomically robust thus, presence of shell is indicative of longterm habitation scale differs between data types Circle proportional to number m -2 for surfclams; bu m -2 for shell : mm surfclams : surfclam shell

10 Differential distribution: surfclam shell versus small surfclams Small surfclams and shell overlap relatively poorly Surfclam shell is taphonomically robust thus, absence of shell is indicative of recent habitation scale differs between data types Circle proportional to number m -2 for surfclams; bu m -2 for shell : mm surfclams : surfclam shell

Differential distribution: cobbles versus large surfclams Cobbles are 2-6 inches across Cobbles are common in the west central portion of the HMA and southeast of Nantucket Large

11 Differential distribution: cobbles versus large surfclams Cobbles are 2-6 inches across Cobbles are common in the west central portion of the HMA and southeast of Nantucket Large surfclams and cobbles overlap relatively poorly scale differs between data types Circle proportional to number m -2 for surfclams; bu m -2 for cobbles : cobbles : mm surfclams

Differential distribution: cobbles versus all (mostly small) surfclams Cobbles are 2-6 inches across Cobbles are common in the west central portion of the HMA and southeast of Nantucket Small

12 Differential distribution: cobbles versus all (mostly small) surfclams Cobbles are 2-6 inches across Cobbles are common in the west central portion of the HMA and southeast of Nantucket Small surfclams and cobbles overlap considerably in the north central portion of the HMA However, at a smaller scale, small surfclams are generally more abundant in areas with fewer cobbles Surfclams are moving into increasingly cobble-rich habitat scale differs between data types Circle proportional to number m -2 for surfclams; bu m -2 for cobbles : cobbles : surfclams

13 Comments on Cobbles Cobbles were normally epibiont free When bionts were present, barnacle scars predominated Cobbles had limited coverage of fast-growing epibionts and almost no coverage of slow growing epibionts Inference: cobbles are rarely exposed; if exposed and colonized, epibionts are rapidly eroded off by prevailing currents/storms Cobbles offer POOR substrate for colonization by attached species and generate limited habitat potential

14 Differential distribution: rocks versus all (mostly small) surfclams Rocks are 6-12 inches across Rocks are frequently encountered in the north and central portion of the HMA and southeast of Nantucket Surfclams and rocks do not overlap consistently However, rocks do not limit surfclam colonization potential scale differs between data types Circle proportional to number m -2 for surfclams; bu m -2 for rocks : rocks : surfclams

15 Comments on Rocks and Boulders Rocks and boulders were normally epibiont free When bionts were present, barnacle scars predominated Rocks and boulders generally had limited coverage of fast-growing epibionts and almost no coverage of slow growing epibionts Inference: rocks and boulders are rarely exposed; if exposed and colonized, epibionts are rapidly eroded off by prevailing currents/storms Rocks and boulders offer POOR substrate for colonization by attached species and generate limited habitat potential

16 Typical surfclam shell (UL), cobble (UR), rock (LL), and boulder (LR) with epibiont free or nearly epibiont free surfaces

Differential distribution: barnacles and barnacle scars versus cobbles Cobbles are 2-6 inches across Barnacles were present at nearly all stations and common at most stations Frequently, barnacles

17 Differential distribution: barnacles and barnacle scars versus cobbles Cobbles are 2-6 inches across Barnacles were present at nearly all stations and common at most stations Frequently, barnacles were identified as barnacle scars Barnacles were attached to rocks, cobbles, shell, mussels, etc. Circle proportional to bu m -2 for cobbles; occasional (1) and common (2) for barnacles scale differs between data types : cobbles : barnacles/barnacle scars

18 How common are barnacles and barnacle scars? Examined Fraction encrusted Shells % Cobbles % Rocks % Boulders % Total 901 Note that photographic analyses are not normalized to substrate catch volume or by station: numbers are raw estimates based on the number of photographs taken Note that substrate photographs emphasize the side with the most attached epibionts

19 How common are barnacles and barnacle scars? Barnacles Barnacle scars Shells 30.0% 51.4% Cobbles 22.7% 59.6% Rocks 28.6% 73.6% Boulders 26.9% 76.9% What makes a barnacle scar: Dissolution slow relative to settlement/growth Physical abrasion/erosion potentially fast relative to settlement/growth Bioerosion bioeroders of proper size are rare

20 Cobbles with barnacles and barnacle scars

Assessment strategy: NMFS Delaware II protocol Miscellaneous epibionts: anemones, tunicates, sponges Station tally: sum of occasional (1) and common (2) designations; maximum value = 6 Epibionts

21 Assessment strategy: NMFS Delaware II protocol Miscellaneous epibionts: anemones, tunicates, sponges Station tally: sum of occasional (1) and common (2) designations; maximum value = 6 Epibionts rarely encountered: maximum tally = 4 Epibionts very rarely encountered where large surfclams were caught Circle proportional to numbers m -2 for surfclams; sum of occasional (1) and common (2) for attached epibionts scale differs between data types Differential distribution: large surfclams versus epibionts : miscellaneous epibionts : mm surfclams

Differential distribution: small surfclams versus epibionts Miscellaneous epibionts: anemones, tunicates, sponges Station tally: sum of occasional (1) and common (2) designations; maximum value = 6

22 Differential distribution: small surfclams versus epibionts Miscellaneous epibionts: anemones, tunicates, sponges Station tally: sum of occasional (1) and common (2) designations; maximum value = 6 Epibionts rarely encountered at any station: maximum tally = 4 Epibionts rarely encountered where small surfclams were caught Circle proportional to numbers m -2 for surfclams; sum of occasional (1) and common (2) for attached epibionts scale differs between data types : miscellaneous epibionts : mm surfclams

23 Comments on attached epibionts: anemones, tunicates, sponges Attached epibionts were rarely encountered and found commonly at very few sites Tunicates were most frequent, with sponges less frequent, and anemones very rare Cobbles, rocks and boulders were usually epibiont free Inference: cobbles, rocks and boulders are rarely exposed; if exposed and colonized, epibionts are rapidly eroded off by prevailing currents/storms; slow growing epibionts have little chance of colonization and growth Cobbles, rocks and boulders offer POOR substrate for colonization by attached species and generate limited habitat potential

24 How common are tunicates, sponges, and anemones? Examined Fraction encrusted Shells % Cobbles % Rocks % Boulders %

25 How common are tunicates, sponges, and anemones? Tunicates Sponges/Anemones Shells 4.8% 0.0% Cobbles 10.1% 1.3% Rocks 7.9% 1.4% Boulders 3.8% 3.8%

26 Examples of he rare large attached epibionts

Differential distribution: hydroids versus cobbles Hydroids refer to erect hydroids and bryozoans, likely mostly hydroids Cobbles are 2-6 inches Hydroids were frequently encountered throughout the

27 Differential distribution: hydroids versus cobbles Hydroids refer to erect hydroids and bryozoans, likely mostly hydroids Cobbles are 2-6 inches Hydroids were frequently encountered throughout the western twothirds of the surveyed area, including the western half of the HMA Hydroids were attached to cobbles, rocks, boulders, shell, mussels, and various living animals such as gastropods Circle proportional to bu m -2 for cobbles; occasional (1) and common (2) or hydroids scale differs between data types : cobbles : hydroids

Differential distribution: hydroids versus large surfclams Hydroids refer to erect hydroids and bryozoans, likely mostly hydroids Hydroids were frequently encountered where large surfclams were

28 Differential distribution: hydroids versus large surfclams Hydroids refer to erect hydroids and bryozoans, likely mostly hydroids Hydroids were frequently encountered where large surfclams were found, unlike most other attached epibionts Hydroids were attached to cobbles, rocks, boulders, shell, mussels, and various living animals such as gastropods Circle proportional to numbers m -2 for surfclams; occasional (1) and common (2) for hydroids scale differs between data types : mm surfclams : hydroids

29 Comments on hydroids No effort was made to distinguish erect hydroids and bryozoans, but most were likely hydroids Hydroids were very common at many sites; they attached to any hard substrate including cobbles, rocks, boulders, surfclam shell, other shell, living gastropods, mussels, etc. Hydroids were resistant to erosion either because they grow faster than the frequency of erosive events or their flexibility allows protection Hydroids are the only common epibiont in areas inhabited by large surfclams Hydroids occurred with greater frequency west of the HMA, but were common in the western portion of the HMA

30 How common are hydroids? Examined Fraction encrusted Shells % Cobbles % Rocks % Boulders %

31 Putative hydroids attached to various substrates

32 Differential distribution: large surfclams versus mussels Mussels were Mytilus cf. edulis and Modiolus modiolus Both species often co-occurred in the same bed; both species were characterized by a dispersed sizefrequency including new recruits and adults Mussels were rarely encountered in large numbers; stations yielding large catches were encountered in the northern panhandle and south central portions of the HMA Large surfclams and mussels rarely occurred commonly at the same station scale differs between data types Circle proportional to number m -2 for surfclams; bu m -2 for mussels : mussels : mm surfclams

33 Differential distribution: small surfclams versus mussels Mussels were Mytilus cf. edulis and Modiolus modiolus Both species often co-occurred; both were characterized by a size-frequency including new recruits and adults Mussels were rarely encountered in large numbers; stations yielding large catches were in the northern panhandle and south central portion of the HMA Small surfclams and mussels rarely occurred commonly at the same station scale differs between data types Circle proportional to number m -2 for surfclams; bu m -2 for mussels : mussels : mm surfclams

34 Differential distribution: cobbles versus mussels Mussels were Mytilus cf. edulis and Modiolus modiolus Both species often co-occurred in the same bed Cobbles were 2-6 inches Mussels were rarely encountered in large numbers; stations yielding large catches were in the northern panhandle and south central portion of the HMA Cobbles and mussels sometimes occurred commonly at the same station, but cobbles were not required to support mussel habitation scale differs between data types Circle proportional to bu m -2 for mussels and cobbles : cobbles : mussels

35 Differential distribution: mussels versus rocks Mussels were Mytilus cf. edulis and Modiolus modiolus Both species often co-occurred in the same bed Rocks are 6-12 inches Mussels were rarely encountered in large numbers; stations yielding large catches were in the northern panhandle and south central portion of the HMA Rocks and mussels sometimes occurred commonly at the same station, but rocks were not required to support mussel habitation scale differs between data types Circle proportional to bu m -2 for mussels and rocks : rocks : mussels

36 Comments on mussels Mussels were very common at a number of sites Mussels did not use cobbles, rocks, or boulders as primary habitat; in fact mussels attached to these sedimentary components were collected very rarely Cobbles, rocks and boulders were usually mussel free Inference: cobbles, rocks and boulders are rarely exposed; if exposed and colonized, mussels are rapidly eroded off by prevailing currents/storms Cobbles, rocks and boulders offer POOR substrate for colonization by mussels and generate limited habitat potential Mussels attach primarily to themselves; beds are weighted down by mussel attachment to pea gravel and sand Erosion velocities to suspend and move mats are reported to be knots; such velocities commonly occur in the survey region, suggesting that mussel mat location may shift over time Surfclams rarely overlap with mussels; however, surfclams are moving into deeper water, suggesting that community replacement is occurring with mussels as it is with ocean quahogs.

37 How common is evidence of mussel attachment? Examined Fraction encrusted Shells % Cobbles % Rocks % Boulders %

38 Above, a cobble and a shell with byssal threads attached. Below, a cobble and a rock with mussels attached

39 A look at the underside of a mussel mat

Differential distribution: sea urchins versus mussels Sea urchins were encountered at only a few sites In most cases, these sites were locations where mussels were also found Sea urchins were most

40 Differential distribution: sea urchins versus mussels Sea urchins were encountered at only a few sites In most cases, these sites were locations where mussels were also found Sea urchins were most common in the central and south central portion of the HMA The occurrence of sea urchins rarely overlapped the occurrence of surfclams Circle proportional to numbers m -2 for sea urchins and bu m -2 for mussels scale differs between data types : mussels : sea urchins

41 Differential distribution: miscellaneous crabs versus mussels Crabs were encountered commonly at only a few sites In most cases, these sites were locations where mussels were also found Crabs were most common in the north central and south central portion of the HMA The occurrence of crabs rarely overlapped the occurrence of surfclams Circle proportional to numbers m -2 for crabs and bu m - 2 for mussels scale differs between data types : mussels : miscellaneous crabs

42 Comments on musselassociated biota Mussels were very common at a number of sites These sites generally supported significant numbers of crabs; sea urchins were frequently encountered Crabs and sea urchins were rarely encountered elsewhere Surfclams rarely overlap with mussels The surveyed region has two primary community types: surfclams and associated sandy biota; mussels and associated mobile epifauna Both are likely in transition as surfclams invade deeper water, potentially displacing mussels Cobbles, rocks, and boulders, though common in the region, do not control or affect community type and location to a significant degree

Differential distribution: naticids versus large surfclams Naticid gastropods were encountered commonly at only a few sites These sites were not associated predictably with high surfclam catches or

43 Differential distribution: naticids versus large surfclams Naticid gastropods were encountered commonly at only a few sites These sites were not associated predictably with high surfclam catches or high mussel catches Naticids were most common in the west central portion of the survey region Circle proportional to numbers m -2 for surfclams and naticids scale differs between data types : mm surfclams : naticid gastropods

44 Differential distribution: naticids versus small surfclams Naticid gastropods were encountered commonly at only a few sites These sites were not associated predictably with high catches of small surfclams Naticids were most common in the west central portion of the survey region Circle proportional to numbers m -2 for surfclams and naticids scale differs between data types : mm surfclams : naticid gastropods

45 Naticids are bivalve predators Comments on naticids Naticids occurred predictably throughout the survey region, with high numbers in certain locations These locations were not consistently associated with high surfclam or high mussel catches; in fact, the distribution of naticids was remarkably unpredictable based on observed megabiota Smaller bivalves (e.g., Astarte, Pitar) were commonly observed but not quantified due to low dredge selectivity; these may be naticid prey

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