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Service Description: The data presented here are summarized from annual National Marine Fisheries Service (NMFS), Southeast Fisheries Science Center (SEFSC) fishery independent Bottom Longline Surveys.The surveys were started in 1995, to assess the distribution and abundance of large and small coastal sharks across their known or suspected ranges. The fishing depths were selected based on commercial shark fishing log summaries, which indicated that the primary depths of effort were 18-73 m (10 to 40 fm). A random stratified sampling design with three depth strata; 18-36 m (10-20 fm), 36-55 m (20-30 fm) and 55-73 m (30-40 fm) were used and uniform effort across contiguous 60 nautical mile sampling zones was achieved. Based on analysis of the first two survey years, the 1997 survey was modified by eliminating depth stratification and changing the survey depths to 10-55 m (5-30 fm). The depth reduction was at the request of the SEFSC to ensure that the full range of several coastal sharks was encompassed by the survey. Elimination of depth stratification was to avoid over-sampling strata which represented the least available habitat (the 30-40 fm strata represented very little of the available bottom, but was receiving 33% of the effort). A significant event in the evolution of our longline surveys occurred in 1999 when we were requested to implement a longline survey targeting red snapper (Lutjanus campechanus). At the time, red snapper were not specifically targeted as part of the shark surveys; a different hook type (circle hook) was used, and different depth strata were sampled. The snapper work was conducted between 64-146 m (35-80 fm) in an area from east of the Mississippi River to south of Perdido Key, Florida. Random sampling without proportional allocation was used and sampling units were 10 nautical mile blocks given the small geographical area to be covered. In 2001, the shark and red snapper surveys were combined into a single annual survey of the U.S. Gulf of Mexico. Proportional allocation based on shelf width within statistical zones was adopted and the survey was stratified by depth with 50% allocation in 9-55 m, 40% allocation from 55-183 m and 10% allocation from 188-366 m. This allocation provided effort in the 9-55 m strata comparable to that achieved in previous shark surveys, thereby preserving the time series back to 1995. The major change in the shark surveys was adoption of the Circle hook as the standard for these surveys. A small longline spool holds approximately 5 nautical mile 4.0 mm diameter monofilament line (900 - 1200 lb; 401.8 - 535.7 kg test); up to 10 nautical miles for large spools. Prior to bottom longline deployment, the mainline is attached to a high flyer (radar reflecting buoy). High flyers are attached at both ends of the deployed mainline for visual reference and to facilitate gear retrieval. As the bottom longline is deployed the vessel’s GPS is used to determine distance covered. Because of the constant cutting and reattachment of the mainline and potential loss of sections of line over the course of a survey, the mainline is not marked in sections and the length of mainline deployed is based on GPS intervals. One-hundred gangions (monofilament leaders with AK snap attachment clip and hook) are attached to 1 nautical mile of mainline approximately equidistantly (about every 60 ft or 31 m) throughout the set. Gangion spacing is determined by GPS (i.e., at 1/10 nautical mile 10 evenly spaced gangions should have been deployed) and nautical mile increments are relayed to the gear set crew by hand-held 2-way radios. An electronic beeper (interval based on vessel speed) is often used to determine component attachment intervals. Weights (5 - 10 kg) are attached to the beginning, middle and end of the bottom longline to prevent gear from rising in the water column, as well as to minimize horizontal movement. After the end weight is attached to the bottom longline gear, the mainline is cut and attached to the second high flyer. Prior to the gear haul back, the mainline is reattached to the remaining line on the spool. Buoy lines (or drop lines) are continuations of the mainline and are not separate gear components but are created by deploying an adequate amount of mainline monofilament for tethering high flyer buoys to the bottom longline gear. Buoys/high flyers are used only on the distal ends without a mid-set buoy. To properly calculate catch per unit effort (CPUE) and a variety of additional statistical analyses, it is important to document longline set, gear soak and longline haul back events. There are 4 critical events; first high flyer deployed (beginning of the set), last high flyer deployed (end of the set), first high flyer retrieved (beginning of haul back) and last high flyer retrieved (end of haul back). Minimum data elements required for each event are the date, time, bottom depth, latitude and longitude. Standard sets are 1 hr in duration with 100 hooks attached along 1 nautical mile of mainline. There are a number of situations that can affect the haul back duration including; high catch rates where data reporting requirements and tagging necessitate slowing the retrieval process, large fish entangling gangions and other gear components, gear entanglement with bottom obstructions and turtle encounters. If the haul back is delayed, some of the hooks deployed near the end of the set soak for more than the 1 hr standard. However, since the time event is recorded for the final high flyer brought aboard to end the haul back, extended haul back times are documented. Gear soak time is an important element in calculating fishing effort (catch per unit effort, CPUE, expressed as the number of captures by species/100 hook hr). Soak time is defined during SEFSC surveys, and often for other surveys, as the time between deployment of the last high flyer to end the set to the time of retrieval of the first high flyer to begin haul back. Since the beginning and end of the soak period are essential data elements, soaks that deviate from the standard 1 hr can be accounted for during data analysis. It is possible to use critical events for re-evaluating effort calculations if needed since the 4 critical events are data elements (begin set, end set, begin haul back and end haul back). Ideally, sets are conducted parallel to depth contours with reasonable effort made to maintain a uniform bottom depth and vessel speed throughout the set. Maintaining a uniform set depth can be difficult and may not be feasible when setting gear along areas of high relief or in high winds or currents. Gear is set from the stern of the vessel and communications between the deck crew and helmsman are maintained via hand held two-way radios. Set procedures are generally standard and should be maintained for consistent effort. Primary set procedures and events include; wheel house to deck notification of the set event, deploying the first high flyer, attachment of the first weight, attaching gangions at approximately equidistant increments, attachment of the mid-weight, completing gangion deployment, attaching the last weight, and deploying the last high flyer to mark the set termination point. Data is summarized here from all Bottom Longline Survey stations fished with circle hooks from 2000 to 2009 by 15 minute longitude by latitude blocks in which sampling occurred. CPUE (number/100 hook hr) data is summarized here from all Bottom Longline Survey stations fished with circle hooks from 2000 to 2009 by 15 minute longitude by latitude blocks in which sampling occurred.

Map Name: Bottom Longline Stations - Fisheries-Independent - Federal

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Layers: Description: TThe data presented here are summarized from annual National Marine Fisheries Service (NMFS), Southeast Fisheries Science Center (SEFSC) fishery independent Bottom Longline Surveys.The surveys were started in 1995, to assess the distribution and abundance of large and small coastal sharks across their known or suspected ranges. The fishing depths were selected based on commercial shark fishing log summaries, which indicated that the primary depths of effort were 18-73 m (10 to 40 fm). A random stratified sampling design with three depth strata; 18-36 m (10-20 fm), 36-55 m (20-30 fm) and 55-73 m (30-40 fm) were used and uniform effort across contiguous 60 nautical mile sampling zones was achieved. Based on analysis of the first two survey years, the 1997 survey was modified by eliminating depth stratification and changing the survey depths to 10-55 m (5-30 fm). The depth reduction was at the request of the SEFSC to ensure that the full range of several coastal sharks was encompassed by the survey. Elimination of depth stratification was to avoid over-sampling strata which represented the least available habitat (the 30-40 fm strata represented very little of the available bottom, but was receiving 33% of the effort). A significant event in the evolution of our longline surveys occurred in 1999 when we were requested to implement a longline survey targeting red snapper (Lutjanus campechanus). At the time, red snapper were not specifically targeted as part of the shark surveys; a different hook type (circle hook) was used, and different depth strata were sampled. The snapper work was conducted between 64-146 m (35-80 fm) in an area from east of the Mississippi River to south of Perdido Key, Florida. Random sampling without proportional allocation was used and sampling units were 10 nautical mile blocks given the small geographical area to be covered. In 2001, the shark and red snapper surveys were combined into a single annual survey of the U.S. Gulf of Mexico. Proportional allocation based on shelf width within statistical zones was adopted and the survey was stratified by depth with 50% allocation in 9-55 m, 40% allocation from 55-183 m and 10% allocation from 188-366 m. This allocation provided effort in the 9-55 m strata comparable to that achieved in previous shark surveys, thereby preserving the time series back to 1995. The major change in the shark surveys was adoption of the Circle hook as the standard for these surveys. A small longline spool holds approximately 5 nautical mile 4.0 mm diameter monofilament line (900 - 1200 lb; 401.8 - 535.7 kg test); up to 10 nautical miles for large spools. Prior to bottom longline deployment, the mainline is attached to a high flyer (radar reflecting buoy). High flyers are attached at both ends of the deployed mainline for visual reference and to facilitate gear retrieval. As the bottom longline is deployed the vessel’s GPS is used to determine distance covered. Because of the constant cutting and reattachment of the mainline and potential loss of sections of line over the course of a survey, the mainline is not marked in sections and the length of mainline deployed is based on GPS intervals. One-hundred gangions (monofilament leaders with AK snap attachment clip and hook) are attached to 1 nautical mile of mainline approximately equidistantly (about every 60 ft or 31 m) throughout the set. Gangion spacing is determined by GPS (i.e., at 1/10 nautical mile 10 evenly spaced gangions should have been deployed) and nautical mile increments are relayed to the gear set crew by hand-held 2-way radios. An electronic beeper (interval based on vessel speed) is often used to determine component attachment intervals. Weights (5 - 10 kg) are attached to the beginning, middle and end of the bottom longline to prevent gear from rising in the water column, as well as to minimize horizontal movement. After the end weight is attached to the bottom longline gear, the mainline is cut and attached to the second high flyer. Prior to the gear haul back, the mainline is reattached to the remaining line on the spool. Buoy lines (or drop lines) are continuations of the mainline and are not separate gear components but are created by deploying an adequate amount of mainline monofilament for tethering high flyer buoys to the bottom longline gear. Buoys/high flyers are used only on the distal ends without a mid-set buoy. To properly calculate catch per unit effort (CPUE) and a variety of additional statistical analyses, it is important to document longline set, gear soak and longline haul back events. There are 4 critical events; first high flyer deployed (beginning of the set), last high flyer deployed (end of the set), first high flyer retrieved (beginning of haul back) and last high flyer retrieved (end of haul back). Minimum data elements required for each event are the date, time, bottom depth, latitude and longitude. Standard sets are 1 hr in duration with 100 hooks attached along 1 nautical mile of mainline. There are a number of situations that can affect the haul back duration including; high catch rates where data reporting requirements and tagging necessitate slowing the retrieval process, large fish entangling gangions and other gear components, gear entanglement with bottom obstructions and turtle encounters. If the haul back is delayed, some of the hooks deployed near the end of the set soak for more than the 1 hr standard. However, since the time event is recorded for the final high flyer brought aboard to end the haul back, extended haul back times are documented. Gear soak time is an important element in calculating fishing effort (catch per unit effort, CPUE, expressed as the number of captures by species/100 hook hr). Soak time is defined during SEFSC surveys, and often for other surveys, as the time between deployment of the last high flyer to end the set to the time of retrieval of the first high flyer to begin haul back. Since the beginning and end of the soak period are essential data elements, soaks that deviate from the standard 1 hr can be accounted for during data analysis. It is possible to use critical events for re-evaluating effort calculations if needed since the 4 critical events are data elements (begin set, end set, begin haul back and end haul back). Ideally, sets are conducted parallel to depth contours with reasonable effort made to maintain a uniform bottom depth and vessel speed throughout the set. Maintaining a uniform set depth can be difficult and may not be feasible when setting gear along areas of high relief or in high winds or currents. Gear is set from the stern of the vessel and communications between the deck crew and helmsman are maintained via hand held two-way radios. Set procedures are generally standard and should be maintained for consistent effort. Primary set procedures and events include; wheel house to deck notification of the set event, deploying the first high flyer, attachment of the first weight, attaching gangions at approximately equidistant increments, attachment of the mid-weight, completing gangion deployment, attaching the last weight, and deploying the last high flyer to mark the set termination point. Data is summarized here from all Bottom Longline Survey stations fished with circle hooks from 2000 to 2009 by 15 minute longitude by latitude blocks in which sampling occurred. CPUE (number/100 hook hr) data is summarized here from all Bottom Longline Survey stations fished with circle hooks from 2000 to 2009 by 15 minute longitude by latitude blocks in which sampling occurred.

Copyright Text: David Hanisko, National Marine Fisheries Service; Jeff Rester, Gulf States Marine Fisheries Commission

Spatial Reference: 102100  (3857)


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