The general specifications for developing the remote attachment device were an extendable pole (i.e., to allow for varying distances between the remote attachment device operator and target animal) with a delivery method powered by an explosive, pneumatic, or spring-loaded system. The force for this system needed to be large enough to pierce an attachment pin through the trailing edge of a rigid, dolphin dorsal fin, and at a speed fast enough to attach the satellite tag on a surfacing, bow-riding small cetacean. The initial design and functionality were hypothesized to be comparable to how a roto-tag is attached to the ear of a livestock animal (i.e., a set of pliers are loaded with the roto-tag, the pliers are squeezed down, the tag goes through the animal’s ear into a locked position, and the roto-tag slides out of the pliers attached to the animal’s ear), which is in part how the initial single-pin, dorsal fin transmitter design was developed [32, 33].
The development of the remote attachment device required a stepwise process, including several phases:
1) Conceptual design: marine mammal researchers and engineers identified the requirements and specifications for the attachment device, including types of material, functionality of parts, and overall method for tag deployment.
2) Prototype development: production of final conceptual design into a functional device to assess appearance, feel, and operation.
3) Stranded (fresh dead) dorsal fin testing: implementation of the device prototype to determine efficacy, functionality, and limitations.
4) In-field testing: real-world assessment to identify likelihood of success for remote deployments and any potential risks to free-swimming, wild small cetaceans.
Conceptual design and prototype development
Six different engineering companies were interviewed to identify which would be appropriate to conduct the conceptual design and prototype development components of this project. Considerations included level of interest in the project, skillsets and expertise, projected timelines for deliverables, and estimated cost. An engineering facility based out of Pittsburg, Kansas, USA (Company A) was selected as this company had a high level of interest in the project, a large, experienced staff of engineers, reasonable time estimate for project completion (6-months) and mid-level cost estimate ($27,900 US: conceptual design through prototype completion; cost estimate range for all companies interviewed: ~$10,000 - $100,000 US). During the conceptual design phase, engineers worked with marine mammal researchers to study the form and function of the remote deployment device and generated 2D and 3D computer-aided designs (CAD) to determine which option had the highest likelihood of success. The first completed design, termed the “C-Clamp,” utilized a pulley system and spring-loaded polycarbonate or steel risers to generate the force required to pierce the dorsal fin and attach the satellite tag (Fig. 2). However, the high number of moving components required for this device to function effectively, and the precise measurements required to consistently line up the risers, attachment pin, and dorsal fin resulted in this prototype being cancelled before a complete version was finalized.
The next conceptual design, termed the “Firing-J,” focused on a significant reduction in moving parts and from the two moving arms in the “C-Clamp” to a singular arm (Fig. 3). The spring-loaded firing-pin for this design would be released as the dorsal fin contacted the “Firing-J” trigger. Although this design had potential over the “C-Clamp,” there were concerns with the overall functionality, including the angle of the attachment pin lining up with the tag, and ultimately this design was cancelled before prototype development began.
The third conceptual design, termed the “U-Handle,” continued to reduce the number of moving components from that of the “Firing-J,” allowed for a modifiable spring to be loaded as the force generator, and the plunger system was at an approximate 90o angle to the dorsal fin, which allowed for a perpendicular insertion of the attachment pin through the dorsal fin. This conceptual design was identified as the best option moving forward and Company A manufactured the prototype two years post-project initiation (Fig. 4).
Stranded (fresh dead) dorsal fin testing
Stranded (fresh dead) bottlenose dolphin dorsal fins were provided by the University of North Carolina Wilmington (UNCW) Marine Mammal Stranding Program and subsequent prototype testing occurred at the UNCW Oriole Burevitch Laboratory. The goals for this phase of the project were to:
1) Determine if the balance/size/weight of the tagging device to the attachment pole were optimal for remote deployments;
2) Assess if the trigger mechanism would successfully release when the tag contacted the trailing edge of the dorsal fin;
3) Evaluate the guide brackets’ robustness and efficacy for increasing the likelihood of remote deployments;
4) Assess if the spring for the attachment pin deployment would be strong enough to pierce through the dorsal fin;
5) Determine if the release mechanism for the attachment pin/plunger would be acceptable for remote deployments; and
6) Identify any other modifications that were necessary while doing hands-on testing with the prototype.
The equipment used for this phase was the remote tag attachment prototype, ‘dummy’ satellite tag, attachment pin, attachment pole, and a dorsal fin from a stranded (fresh dead) bottlenose dolphin mounted in an upright position to a necropsy table for remote tag prototype testing (Figs. 4 and 5). The initial assessment concluded that the overall functionality of the prototype with regards to the balance/size/weight of the device, the response of the trigger mechanism, robustness of the guide brackets, and the release mechanism were all acceptable. However, significant, additional force was required to pierce the attachment pin through the dorsal fin. To address this concern, the largest sized spring that could fit within the specifications of the prototype was manufactured and additional spacers were added to the trigger to increase the force delivered of the attachment pin. While this modification did increase the force to the pin, it was still not adequate to ensure that the dorsal fin was consistently pierced, and the tag attached.
At this stage in the development process, Company A did not have the resources to collaborate on additional modifications to the prototype, and as a result of these limitations, in addition to a significant delay in prototype completion (1.5 years greater than initial deadline), another engineering facility was engaged moving forward. Company B, based out of Castle Hayne, North Carolina, USA, was an engineering and fabrication facility that had experience with manufacturing various remote biopsy sampling tools for marine mammals and was in close proximity to where stranded dorsal fin testing was occurring (UNCW, Wilmington, North Carolina, USA), which allowed for a higher level of in-person interactions throughout the prototype development process. In working with Company B engineers, the estimated maximum force generated by the spring-loaded prototype was ~40 kg of which a minimum of ~80 kg was necessary for consistent piercing of the dorsal fin for tag attachment. Based upon these force requirements, the decision was made to switch from a spring-loaded to a pneumatic system for the remote attachment prototype. Company B fabricated a pneumatic cylinder with c-frame holder in less than one month to conduct the first round of stranded dorsal fin testing, of which the force generated (~80 kg), reliably delivered the attachment pin through the dorsal fin (Fig. 6). It was recognized at this time that the cylinder needed to be much faster (i.e., must fully deploy a few milliseconds after the dorsal fin makes contact with the firing pin) to work successfully in the field, and cylinders with increased pneumatic pressure were investigated. Unfortunately, Category 5 Hurricane Dorian hit the coast of North Carolina in September 2019 and caused immense damage to Company B’s facility, which delayed further prototype development until early 2020. During February 2020, the COVID-19 pandemic began, and Company B was forced to close for the next year. As a result, the final remote tag attachment prototype with pneumatic system was not completed within the required project deadlines.
In-field feasibility testing
To determine the feasibility for a researcher to line up the trailing edge of a bow-riding dolphin’s dorsal fin with the 30-mm width bracket of the remote attachment device, several possible locations of the tagger’s positioning were investigated, including from:
1) The forward section of the vessel, deploying the tag using an approximate 45-degree downward motion;
2) A bowsprit, deploying on dolphins directly below using a swinging motion; and
3) The sponsons, in the very forward part of the vessel, deploying the tag from behind the dolphin.
Between 30 September – 4 October 2019, a field team consisting of four researchers, using a 6.3 m, center‐console, Zodiac (Zodiac Milpro International, Paris, France) rigid‐hulled inflatable boat with twin 90 hp Yamaha four‐stroke outboard engines, surveyed the coastal waters of the Gulf of Mexico off Panama City Beach, Florida. A 3D acrylonitrile butadiene styrene (ABS) printed version of the tagging bracket was fabricated and mounted to a 1 – 3 m extendable pole with a GoPro Session (GoPro Inc., San Mateo, California USA) to document attempts in lining up the bracket with the trailing edge of free-swimming dolphin dorsal fins and subsequent behavioral responses (Fig. 7). Five days of field effort were conducted, in which a total of 36 sightings were recorded, including 205 coastal bottlenose dolphins and two Atlantic spotted dolphins. Eight attempts were made to line up the tagging bracket with the trailing edge of the dorsal fin, in which three were successful, three were glances, and two were misses. Dolphin responses to all tagging attempts included a tail slap followed by an acceleration away from the bow of the research vessel. Three different types of vessel approaches to bracket testing were conducted (all in excellent water visibility):
1) Slow bow-riding (~5 km/hr): animals were giving slow, predictable surfacings; highest likelihood of remote tagging success;
2) Fast bow-riding (~10 km/hr): animals were giving faster and erratic surfacings; lower likelihood of remote tagging success; and
3) Slow pursuit (~5 km/hr): animals were travelling or socializing and allowing the research vessel to get in close proximity; variable likelihood of remote tagging success depending on individual animals and behavioral state.
The results of the in-field feasibility testing concluded that the 30-mm width of the tagging bracket would be effective in successful tagging attempts with the current prototype specifications. In addition, using a 6.3 m, center‐console, rigid‐hulled inflatable boat was an appropriate tagging vessel in which small cetaceans routinely bow-rode and surfaced in positions that were accessible for tagging attempts. Vessel approaches of slow bow-riding (~5 km/hr) produced the highest likelihood of remote tagging success. The optimal tagger positioning for “lining up” the tag attempt was on the sponsons, in the very forward part of the vessel, and deploying the tag from behind the dolphin. This location allowed the researcher to quickly move into the appropriate tagging position as the dolphin surfaced. It also required very little modification to the vessel and reduced the risk of a standing tagger falling overboard.