NOAA Tech Memo NE 181: Characterization of the Fishing Practices and Marine Benthic Ecosystems of the Northeast U.S. Shelf, and an Evaluation of the Potential Effects of Fishing on Essential Fish Habitat
6. VULNERABILITY OF ESSENTIAL FISH HABITAT TO BOTTOM-TENDING FISHING GEARS
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INFORMATION NEEDS AND SOURCES
This section evaluates potential adverse effects of bottom-tending fishing gears on benthic EFH in the Northeast Region. These gears are regulated by the MSA and the EFH final rule, 50 CFR 600.815(a)(2)(i). The EFH final rule recommends that the evaluation consider the effects of each fishing activity on each type of habitat found within the EFH for any affected species and life stage. The EFH rule further recommends that the following information be reviewed in making an evaluation: 1) intensity, extent, and frequency of any adverse effects on EFH; 2) the types of habitat within EFH that may be adversely affected; 3) habitat functions that may be disturbed; and 4) conclusions regarding whether and how each fishing activity adversely affects EFH.
The EFH final rule requires that EFH designations be based on the best available information. This information may fall into four categories that range from the least specific (Level 1) to the most specific (Level 4). These categories are defined as follows:
Level 1: Presence/absence data are available to describe the distribution of a species (or life history stage) in relation to potential habitats for portions of its range.
Level 2: Quantitative data (i.e., density or relative abundance) are available for the habitats occupied by a species or life history stage.
Level 3: Data are available on habitat-related growth, reproduction, and/or survival by life history stage.
Level 4: Data are available that directly relate the production rates of a species or life history stage to habitat type, quantity, and location.
Existing EFH designations in the Northeast Region are based primarily on Level 2 information. This level of information is inadequate for making definitive determinations of the consequences of fishing-related habitat alterations on EFH for any species or life stage in the region because the habitat alterations caused by fishing cannot be linked to any known effect on species productivity. Therefore, this section of the document qualitatively evaluates the vulnerability of benthic EFH for each species and life history stage in the region to the effects of bottom-tending fishing gear. Vulnerability is defined as the likelihood that the functional value of benthic EFH would be adversely affected by fishing. Further, given the limited nature of the information available for this qualitative evaluation, emphasis was placed on the identification of potential adverse effects of fishing on benthic EFH.
Information used to perform these evaluations included: 1) the EFH designations adopted by the Mid-Atlantic, New England, and South Atlantic Fishery Management Councils; 2) the results of a Fishing Gear Effects Workshop convened in October 2001 (NREFHSC 2002); 3) the information provided in this document, including the results of existing scientific studies, and the geographic distribution of fishing gear use in the Northeast Region; and 4) the habitats utilized by each species and life stage as indicated in their EFH designations and as supplemented by other references. In most cases, habitat utilization was determined from the information provided in the EFH Source Documents (NOAA Technical Memorandum NMFS-NE Issues 122-152, 163, and 173-179), with additional information from Collette and Klein-MacPhee (2002).
EVALUATION METHODS AND RESULTS
Vulnerability of EFH to bottom-tending fishing gear was ranked as none, low, moderate, or high, based on a matrix analysis of three primary components: 1) benthic life stages of FMP-regulated species; 2) habitat function and sensitivity; and 3) gear usage. The matrix analysis initially ranked each habitat for its susceptibility to disturbance and each gear for its potential adverse effects, and then subsequently combined those two rankings with available information on the habitat usage by species/life stages and the distribution of gear usage, in order to obtain the EFH vulnerability rankings.
These evaluations are summarized in Table 6.1. Note in Table 6.1 that: 1) species and life stages for which EFH vulnerability was "not applicable" are not included; and 2) pots, traps, sink gill nets, and bottom longlines -- to which the EFH of all species and life stages showed "low" vulnerability -- are also not included.
The rationale for these evaluations is outlined by species in Tables 6.2-6.45, and was based on the authors' following three assumptions. First, the habitat's value to each species and life stage was characterized to the extent possible based on its function in providing shelter, food, and/or the right conditions for reproduction. For example, if the habitat provided shelter from predators for juvenile or other life stages, gear effects that could reduce shelter were of greater concern than other effects. Second, in cases where a food source was closely associated with the benthos (e.g., infauna), the ability of a species to use alternative food sources (e.g., generalist versus specialist species) was evaluated. Third, since benthic prey populations may also be adversely affected by fishing, gear effects that could reduce the availability of prey for bottom-feeding species or life stages were of greater concern than if the species or life stages were piscivorous.
The information in Tables 6.2-6.45 includes for each life stage the geographical extent of EFH, its depth range, its seasonal occurrence, and a brief EFH description that includes -- for benthic life stages -- substrate characteristics. The information presented in columns 2-5 of these tables is derived from EFH text descriptions and maps that originally appeared in the NEFMC Omnibus EFH Amendment (NEFMC 1998) and several FMPs prepared by the NEFMC and MAFMC. Additional information, where available, is provided at the bottom of each table to explain the rationale that was used in making the gear-specific EFH vulnerability rankings. EFH descriptions of depth, seasonal occurrence, and habitats (columns 3-5 in Tables 6.2-6.45) are not always consistent among life stages of an individual species. Spawning American plaice adults, for example, are described as occurring from March through June, but their eggs are described as occurring from December through June on Georges Bank (Table 6.2). In addition, the information in columns 3-5 in some cases does not completely agree with the information provided in the rationale.
The rest of this section details the methods that were used to perform the evaluations and assign the rankings.
Five life stages were evaluated: eggs, larvae, juveniles, adults, and spawning adults. Adult and spawning adult life stages were in most cases combined for evaluation purposes due to the difficulty in distinguishing between the two. In some cases (e.g., pelagic life stages that are not vulnerable to bottom-tending fishing gear effects), a vulnerability ranking was not applicable.
Habitat Scoring and Ranking
Habitat rank was determined from four criteria that were qualitatively evaluated for each life stage based on existing information. Each evaluation resulted in a score based on predefined scoring criteria.
The first three criteria were related to habitat function, and included shelter, food, and reproduction. The fourth criterion was habitat sensitivity. Scoring of these criteria was determined as follows:
Shelter (scored from 0 to 2): If the life stage is not dependent on bottom habitat to provide shelter, then it was scored a 0. Almost every life stage evaluated has some dependence on the bottom for shelter, so, with the exception of a few egg stages, 0 was seldom selected. If the life stage has some dependence on unstructured or noncomplex habitat for shelter, then it was scored a 1. For example, flatfishes that rely primarily on cryptic coloration for predator avoidance, or on sand waves for refuge from bottom currents, were scored a 1. If the life stage has a strong dependence on complex habitats for shelter, then it was scored a 2. For example, juvenile Atlantic cod and haddock, which rely heavily on structure or complex habitat for predator avoidance, were scored a 2.
Food (scored from 0 to 2): If the life stage is not dependent on benthic prey, then it was scored a 0. For example, eggs were always scored a 0, as were life stages that fed exclusively on plankton. If the life stage utilizes benthic prey for part of its diet, but is not exclusively a benthic feeder, then it was scored a 1. For example, species feeding opportunistically on crabs as well as squid or fish were scored a 1. If the life stage feeds exclusively on benthic organisms and cannot change its mode of feeding, then it was scored a 2.
Reproduction (scored from 0 to 1): Limited knowledge of spawning behavior and habitat usage for many species made this the most difficult category to assess. In the opinion of the authors, the available information was insufficient to evaluate this criterion beyond a simple yes or no, resulting in a scoring of 0 or 1 for this factor. While this two-level scoring instead of three-level scoring may have unavoidably undervalued reproduction for some species in the overall scoring, it was decided that this was better than attempting to make finer distinctions that were unsupportable based on available evidence.
A score of 0 was selected for nonreproductive life stages (larvae and juveniles), and for species that are known to spawn in the water column and have only pelagic early life stages. A score of 1 was selected for species where a known association with the bottom exists for one or more aspects of the reproductive cycle.
Habitat Sensitivity (scored from 0 to 2): This criterion does not evaluate the function of the habitat, but instead accounts for its overall relative sensitivity to disturbance. The type of benthic habitat (defined primarily in terms of depth, energy regime, and substrate) inhabited by each species and life stage was based primarily upon its EFH designation.
If a habitat was not considered sensitive to disturbance, then it was scored a 0. However, a score of 0 was not used for any benthic habitat type. If the habitat was considered to have a low sensitivity to disturbance, then it was scored a 1. For example, habitats that are high-energy environments without structural complexity, or that have rapid recovery rates, were scored a 1 (e.g., high-energy sand environments). If the habitat type was considered highly sensitive to disturbance, then it was scored a 2. For example, habitats that are structurally complex (e.g., those supporting epibenthic communities or those with boulder piles), or that have very slow recovery rates (e.g., low-energy deepwater environments), were scored a 2.
These scores were based on existing conceptual models that show a direct relationship between higher structural complexity of the habitat, longer recovery time, and increased vulnerability to disturbance (NREFHSC 2002; NRC 2002).
Habitat rank was defined as the sum of the scores for the four habitat criteria (shelter + food + reproduction + habitat sensitivity). Another way to characterize the habitat rank is the relative vulnerability of the habitat to non-natural physical disturbance. The habitat ranks ranged from 0 to 7, with 7 being the most vulnerable.
Gear Types, Scoring, and Ranking
Five fishing gear classifications were evaluated: otter trawls, New Bedford-style scallop dredges, hydraulic clam dredges, pots and traps, and sink gill nets and bottom long lines. The pot/trap and net/line gear types were considered to have the least effect of the five gear types evaluated. The panel of experts that met in October 2001 ranked their concerns over effects from fixed bottom-tending gear well below their concerns over the effects from mobile bottom-tending gear (NREFHSC 2002). Based on the limited information available (Eno et al. 2001; NREFHSC 2002), the vulnerability of all EFH for all benthic species and life stages to pot and trap usage was considered to be low. Similarly, there is little scientific information that evaluates the effects of sink gill nets and bottom longlines on benthic marine habitats, and none evaluates these effects in the Northeast Region. Consequently, like pots and traps, the vulnerability of all EFH for all benthic species and life stages to sink gill net and bottom longline usage was considered to be low. These rankings should be revisited as more information on gear effects becomes available.
The greatest concern is for the vulnerability of benthic EFH to mobile bottom-tending gears (see Chapters 3 and 4). In the northeastern United States, these gear types include various types of bottom otter trawls, New Bedford-style scallop dredges, and hydraulic clam dredges. Otter trawls are responsible for most of the fisheries landings throughout the Northeast Region, and are used in a variety of substrates, depths, and areas. Scallop dredges are used in sand and gravel substrates. Hydraulic clam dredges are used only in sand, shell, and small gravel within well-defined areas .
Rather than rate the relative effects of these three gear types on EFH, they were treated as having similar effects. The criterion for each gear type was based on the spatial distribution of gear use (scored from 0 to 2) in areas designated as EFH for a given species and life stage. If the gear is not currently used within the EFH area, then it was scored a 0. If the gear is currently used in only a small portion of the EFH area, then it was scored a 1. If the gear is currently used in more than a small portion of the EFH area, then it was scored a 2.
The spatial distribution of fishing activity for each gear was determined from reports of the number of days absent from port, or the days fishing, for individual TMSs of latitude and longitude during 1995-2001 (see Chapter 4). Maps of TMSs designated as EFH are available in NEFMC (1998) and in various fishery management plans developed by the Mid-Atlantic and South Atlantic Fishery Management Councils, and have not been reproduced for this document.
The gear rank assesses the overall effect on EFH from fishing with bottom trawls, scallop dredges, and clam dredges. This gear rank was defined as the product of the habitat rank and the gear distribution score. This relationship was chosen in order to ensure that the EFH vulnerability from gears not used in a particular habitat (i.e., gear distribution = 0) would be 0, or, no effect.
EFH Vulnerability Ranking
Based on natural breaks in the frequency distribution of the gear rankings, the following vulnerability categories were defined:
0 = no vulnerability to the gear. This score could only be attained if the gear was not used in the habitat (gear distribution = 0).
1-6 = low vulnerability to the gear. This score generally occurred where the gear has minimal overlap with EFH (gear distribution = 1) and habitat rank was <7. Additionally, low vulnerability scores occurred in habitats with high gear overlap (gear distribution = 2) and habitat rank was 3.
7-9 = moderate vulnerability to the gear. This score typically occurred where gear overlap with EFH was high (gear distribution = 2) and habitat rank was 4, or, overlap with EFH was low (gear distribution = 1) and habitat rank was 7.
10-14 = high vulnerability to the gear. This score occurred only if the gear overlap with EFH was high (gear distribution = 2) and the habitat rank was 5.