The Great Scallop Search; Pensacola Bay 2023

Introduction

Bay scallops (Argopecten irradians) have been an important part of the economy of many gulf coast communities within the Florida Big Bend for decades.  It was once abundant in all gulf coast counties of the state but beginning in the 1960s populations in many bays began to decline to levels where they are all but nonexistent.  The cause of this decline has been associated with many factors including a decline in water quality, a decline in suitable habitat (sea turtle grass beds – Thalassia), and overharvesting.  Most likely the cause included all of these.  Since the collapse of both the commercial and recreational fishery, Gulf coast communities have been trying to address all three of the stressors above.  Multiple monitoring projects are ongoing in the Pensacola Bay area and one of those is the Great Scallop Search.  

The Great Scallop Search was developed by Sea Grant Agents in Southwest Florida and expanded, through Florida Sea Grant, to Northwest Florida.  In each location volunteers snorkel a 50-meter transect line searching for live bay scallops, as well as monitoring the status of the seagrass habitat.  Since 2015 317 volunteers have logged 634 hours surveying 407 50-meter transects in 106 grids in Big Lagoon or Santa Rosa Sound.  In that time 4 live scallops have been logged, though we hear anecdotal reports of additional scallops being found in these bodies of water. 

Survey Method

Volunteers select and survey one of 11 grids in Big Lagoon, or one of 55 grids in Santa Rosa Sound.  Once on site, the volunteers anchor and record preliminary information on the data sheet provided.  Two snorkelers enter the water and swim on opposite sides of a 50-meter transect line searching for live scallops.  Any live scallop found is measured and returned.  The species and density of the seagrass is recorded as well as the presence/absence of macroalgae on that seagrass.  Four such transects are surveyed in each grid. 

2023 Results

2023	SRS	BL	Total	Other
# of volunteers			72	No significant difference between 2022 and 2023
# of grids surveyed	8	8	16	Slight decrease from 2022.  16 of the 66 grids (24%) were surveyed.
# of transects surveyed	26	51	77	A decrease from 2022.  More surveys were conducted in Big Lagoon than Santa Rosa Sound.
Area surveyed (m2)	2600	5100	7700	1.9 acres
# of scallop found	2	2	4	Four live scallops are a record for this project.  It equals the sum of all other live scallops since the project began.
Scallop Size (cm)	4.5, 5.0	4.0, 4.5
Surveys with Seagrass
Halodule	5	12	17	17/21 surveys – 81%
Thalassia	8	11	19	19/21 surveys – 90%
Syringodium	0	2	2	2/21 surveys – 10%
Grass Density
100% grass	3	9	12	12/21 surveys (57%) were 100% grass
90%	1	0	1	Note: Volunteers typically select area for transects
75%	3	1	4	with a lot of grass.
70%	1	0	1
50%	3	9	12
5%	1	0	1
Macroalgae
Present	4	4	8
Absent	2	10	12	12/21 surveys (57%) had no macroalgae.
Abundant	2	2	4
Sediment Type
Mud	0	1	1
Sand	7	8	15	15/21 surveys (71%) were sandy.
Mixed	1	4	5

21 surveys were conducted covering 16 grids.  8 grids were surveyed in each body of water. 

A total of 77 transects were conducted covering 7,700 m² and four live scallops were found. 

Two of the scallops were found in Big Lagoon and two in Santa Rosa Sound. 

All scallops measured between 4-5cm (1.6-2”). 

The number of live scallops found this year equaled the total number found over the last eight years. 

Most of the transects included a mix of Halodule and Thalassia seagrass ranging from 100% coverage to 5%.  The majority of the transects were between 50-100% grass.  Four transects had 100% Thalassia.  Three of those were in Santa Rosa Sound, one was in Big Lagoon.  The diving depth of the volunteers ranged from 0 meters (0 feet) to 2.4 meters (8 feet).  Macroalgae was present in 8 of the 21 surveys (38%) but was not abundant in most. 

Summary of Project

Year	Volunteer	Grids Surveyed	Transects Surveyed	Live Scallops Found
2015	87	28	101	0
2016	96	31	111	1
2017	5	4	16	0
2018	20	7	32	0
2019	13	6	20	0
2020	5	2	16	1
2021	17	6	24	0
2022	74	22	87	2
2023	72	16	77	4
TOTAL	317		407	8
MEAN	35	14	45	0.4

To date we are averaging 35 volunteers each event, surveying 14 of the 55 possible grids (25%).  We are averaging 45 transects each year (4500 m²), have logged 407 transects (40,700 m²) and have recorded 8 live scallops (< than one a year). 

Discussion

Based on the results since 2016 this year was a record year for live scallops.  Whether they are coming back on their own is still to be seen.  Being mass spawners, bay scallop need high densities in order to reproduce successfully, and these numbers do not support that.  The data, and comments from volunteers, suggest that the grasses look good and dense.  Thalassia, a favorite of the bay scallop, appear to be becoming more abundant.  This is a good sign.