Saco Bay Scallop Stock Enhancement Project

A Collaboration: Northwest Atlantic Marine AllianceLocal fishermen University of New England Maine Sea GrantMaine Department of Marine ResourcesBill Lee, F/V Ocean Reporter

NAMA has spearheaded wild scallop stock enhancement efforts in Saco Bay since 2000, including scallop bed characterization, spat collection, bed reseeding and environmental monitoring.

In the fall of 2000, a group of 22 fishermen and family members (members of the Saco Bay Alliance from Saco, Old Orchard Beach and Scarborough) joined together to undertake wild scallop spat collection

Original Project Possibly too ambitious

Null Hypothesis 1: Reseeding has no effect on restoration of former scallop beds.

Null Hypothesis 2: Seeding density has no effect on scallop survival and growth.

Null Hypothesis 3: Substrate has no effect on reseeding success.

Revised Project Null Hypothesis 1: There is not significant

migration of spat once seeded on the bottom

Null Hypothesis 2: Spat migration does not vary with bottom habitat type

Null Hypothesis 3: Presence of starfish does not have a significant impact on survival of scallop spat

Site 1 was considered by participating commercial scallop divers to be ‘ideal’ scallop habitat Numerous adult scallops of different sizes

were observed, as well as lobsters, crabs, starfish, and snails.

The bottom was shell and pebble, with a thin layer of mud cover in some areas, and characterized by sand waves approximately 10 inches apart and burrows associated with bottom-living animals.

The site occurs near a transition from rough-grain size to a bordering area of sand where adult scallops are not found.

Depth was approximately 40-45 ft.

The second “good habitat” site (Site 2) was close to Site 1 Was characterized by a similar bottom type

and species mix, but without adult scallops (scallop shells were visible, but no live scallops) and more crabs .

Was slightly deeper (45-50 ft) than Site 1 Had a ‘harder packed’ bottom lacking sand

waves, which could indicate a differing bottom current or wave regime.

Site 3 was expected to be less conducive to spat survival. Although in a similar depth (35-45 ft), this site

was in an area of fine, muddy sediment without much marine life ( ‘dead zone’).

Divers described bottom as silty clay with a white stagnant film in patches over some of the area and many burrows.

Some surf clams, razor clams, tube worms, anemones, and a few small crabs (2-4 inches) were observed.

Experimental Design We used a series of replicated treatments

involving different types of enclosures to isolate specific influences on survival of seeded spat, including spat migration predation by starfish

The six experimental treatments (labeled A-F) were intended to control spat and predator movement in different ways.

Label Design Intention

A No enclosure – circular marker on bottom

Control, spat and predators move freely

B Cylindrical enclosure – no lid Spat movement limited, barrier to some predators, not others

C Cylindrical enclosure with one open side – no lid

Spat movement less limited, predator movement less limited

D Cylindrical enclosure with lid Spat movement extremely limited, predator access to spat very low

E Cylindrical enclosure with low density starfish (2 starfish) - no lid

Spat movement limited, predators have easy access to spat (at low predator density)

F Cylindrical enclosure with high density starfish (10 starfish) – no lid

Spat movement limited, predators have easy access to spat (at high predator density)

The experiment worked mostly as planned

There were however, some aspects of the study that were problematic, including unforeseen issues with regards to timing, filming, and weather.

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Conclusions Null Hypothesis 1: There is not

significant migration of spat once seeded on the bottom As noted above, our data indicate that

in fact there was significant migration of spat once seeded on the bottom.

Null Hypothesis 2: Spat migration does not vary with bottom habitat type The number of spat in the enclosures declines

over time at all sites, but there may have been a less rapid decline at Site 1 than at Site 2, and with decline most rapid at Site 3.

This result would be in line with fishermen’s expectations that Site 1 comprised ‘ideal scallop habitat’, Site 2 was ‘good’ and Site 3 was ‘bad’ habitat.

Null Hypothesis 3: Presence of starfish does not have a significant impact on survival of scallop spat The results of our field study were

highly surprising in this regard, as the seeded starfish almost all exited the enclosures rapidly after seeding.

One puzzling result, shown in Figure 5, is that the treatments with starfish (E and F) actually had the highest final numbers of spat. The answer to this puzzle is likely that the

starfish moved out of the enclosures so quickly (as noted by divers and on video), that treatments E and F may really have been equivalent to treatment B.

Other potential predators (including crabs, flounder, and moon snails) were present in the study area, even moving in and out of some enclosures.

Crabs were present unevenly and not controlled within and around enclosures, but appeared attracted to structure of experimental gear (cinderblocks, enclosures).